Ubisoft Connect integration GUIDE / recover games after Proton switching / all games now only work with UC + Proton 8.0-5 / 7.0-6 NOP

UPDATE:
'Ubisoft Connect' itself now works with Proton 8.0-5 to Experimental, provided that the Steam client has been switched to "Offline Mode" before. There are some things to consider and a few manual steps are required during installation, though.

I've worked out a guide, how to add 'UbisoftConnect' to Steam's game library (and integrate existing Ubisoft game installations) - this should work more predictably, at least it does with my setup - and also found and documented some Caveats and required manual steps not considered before, see below.

Also, previously, 'Assassin's Creed Black Flag' and 'Syndicate' would only work with Proton 7.0-6.
Now, there seems to be a regression in either Proton 7.0-6, or 'UbisoftConnect' - they won't work together anymore (UC hangs at startup, with Proton 6.x it will crash).

Instead, Proton 8.0-5 now seems to be the working stable version of choice by now, for both 'Assassin's Creed' Branches, as well as for 'Far Cry 3, 'Blood Dragon' and 'Primal'.

I managed set up and run 'Assassin's Creed Black Flag' with Proton Experimental on another prefix as well. It showed an old 'stuttering' graphics rendering glitch after some time playing, though, as I reported here:

ACBF Thread. Whether this would also occur on P8.0-5, I cannot yet confirm.

'Ubisoft Connect' to Steam Library installation/integration guide:

1. Get the latest 'UbisoftConnectInstaller.exe' from Ubisoft
2. switch Steam to 'Offline Mode' (ports may conflict with 'UbisoftConnect' during its installation and Update)
3. save 'UbisoftConnectInstaller.exe' to the desired target folder, e. g. ~/games/Uplay
4. run SteamClient > Library > Click 'Add a Game' (left lower corner)
5. Click 'Add a non-Steam Game' > Click 'Browse' > ~/games/Uplay/UbisoftConnectInstaller.exe
6. in 'Games' right-click on 'UbisoftConnectInstaller.exe' > 'Properties' > 'Compatibility' > set 'Force the use of a specific Steam Play compatibility tool' > choose 'Proton Experimental'
7. run 'UbisoftConnectInstaller.exe' > choose parent install folder '~/games/Uplay/' > OK > wait for installation + Update + re-launch
8. in 'UbisoftConnect' > Games (Library) > for your already-installed Games each:
   a) click '...' > 'Properties' > 'Installation' > click 'Find installed Game'
   b) choose Game folder location, e. g. 'Workstation > I: > /Uplay/Assassin's Creed IV Black Flag' > OK > wait... > Close
   c) (optional: verify Game files, if errors occur during start or playing the Game)
   d) (optional: in UC click Profile > Settings > General + Notifications + UI > click away Ad + Social BS + Crashreports + UC In-Game UI + Account Linking reminder)
9. run and wait for Games to update, check if everything works
10. Profile > Leave (close UC)
11. in Steam Games > right-click UC > Properties > Shortcut > change 'Target' link from Installer to e. g. '"/media/USER/games/Uplay/Ubisoft Game Launcher/UbisoftConnect.exe"' and 'Start in' to '"/media/USER/games/Uplay/Ubisoft Game Launcher/"' (MIND THE SURROUNDING DOUBLEQUOTES, IF PATHS CONTAIN SPACES, OR ELSE UC WILL NOT RUN!) > rename Shortcut to 'Ubisoft Connect'
12. close Properties and re-run UC, wait for Updates (when it hangs at 1st try, close UC and re-run), check if everything runs again

The problem is obviously, that Steam doesn't recognize the nature of the 'UbisoftConnectInstaller', or more precisely, it only allows to run an executable once, at the time where 'Add a non-Steam Game' creates a new prefix, which is done explicitly for UC, not the games themselves - these will be installed by UC / into a custom folder and always run with the Proton version, the UC prefix was configured with.

Plus, the executable and execution folders in Steam's UC entry will not get automatically updated to the real installation subfolder and double-quoted accordingly - this needs to be done manually, after UC was installed.

If Steam allowed for creating a Proton prefix first, THEN running executables in it multiple times, life could be easier, e. g. for installation scenarios like this and also for manual installation of upgrades and similar, as Winetricks allows. There's a project called 'Protontricks', but Steam hasn't integrated any of its' features.

All your installed games and progress will vanish, after switching forth and back to and from another Proton version for UC's prefix, like to 8.0-5 and back, although the game files and data are still in place - you can get them back the same way, as described under 6), provided, the prefix isn't damaged by this action, or by running the Installer in it again.

For the 'AC' titles, Steam places them under the corresponding Proton prefix, with which 'Ubisoft Connect' was running at the time, the game was installed, e. g. into:
/media/.../Steam/debian-installation/steamapps/compatdata/3630262936/pfx/drive_c/users/steamuser/Documents/...

For the 'FC' titles, they go into:
/.../Documents/My Games/...

For 'Ubisoft Connect' and a few games, some configurations are also stored under:
/media/.../steamuser/AppData/Local/My Games/...
.../Ubisoft Game Launcher/
.../Far Cry 3/

There'll be a separate prefix for every Proton version tested with the 'Ubisoft Connect' installation, including configurations for all corresponding games activated with it, likewise.

If unsure, which prefix folder belongs to what, check the file 'version' directly under the prefix' parent folder (named only with a number), e. g.:
/media/.../Steam/debian-installation/steamapps/compatdata/3630262936

The actual 'Ubisoft Connect' and game installations may reside on another partition e. g. in:
/media/USER/games/Uplay/...
.../Ubisoft Game Launcher/ (where Ubisoft Connect stores game configurations, creds, savegames and more)
.../Far Cry 3/
...

You should always switch Steam to 'Offline Mode', before running UC, or have the latter turned to 'Offline' before last time closing - it but has no real 'Offline Mode', though.

Generally, 'UbisoftConnect' itself feels clunky, the buttons will respond laggy and have serious focus and minor rendering issues.

To run my 'Far Cry' AND 'Assassin's Creed' games, I'll need to use Proton 8.0-5 for UC, currently, it seems to be the only working combination for all my UPlay games - the 'Far Cry' titles currently will work with Proton Experimental, though. There's some DirectX11 crashing issue with FC3 in any case - see below.

EDIT:
After installing 'Ubisoft Connect' again in a Proton Experimental prefix and running Far Cry 3 from there, the game would start once, with low resolution. After setting any graphics options that trigger a restart, e. g. setting correct native resolution (1920x1080), or after manually re-starting after 1st start, FC3 will crash.

After that, the game keeps hanging at the FC3 boot logo, with animated circle icon. After checking game files in Uplay, the game would try to re-install 'Microsoft Visual C++ 2008 Redistributable - x86 9.0.30729.17' and 'Microsoft Visual C++ 2010 x86 Redistributable - 10.0.40219'. Then, same symptom again.

CAUSE AND TEMPORARY WORKARAOUND:

The reason seems to be a problem with DirectX11 (on by default), or any graphics option it activates. When FC3 crashes, the following property needs to be set in

/media/.../Steam/debian-installation/steamapps/compatdata/3630262936/pfx/drive_c/users/steamuser/Documents/My Games/Far Cry 3/TutorialProfile.xml

UseD3D11="0"

This results in a fallback to DirectX9, with which the game will eventually run. So, either a DirectX11 dependency isn't fulfilled (e. g. missing DLL, or Redistributable), or there's a bug in either Proton/Wine's or FC3's implementation.

Interestingly though, setting DirectX11, 'ULTRA' quality, MSAA 8 and HDAO in 'Far Cry: Blood Dragon' - which should have the same technical base than FC3, with the same engine - works fine without crashing.

SIDE NOTE:
Upon installing and launching 'Assassin's Creed Unity', the game would start 'Updating' right after starting a new campaign, at high gc engine / 250W energy consumption and ~1 of 50% per minute update speed (presumably loading precompiled shaders or similar) - really, who's implementing such lunatic crap features?

The issue names no Proton source file or test and combines installation guidance with several Ubisoft Connect and game failures. Start by isolating one reproducible symptom, such as the Far Cry 3 crash associated with TutorialProfile.xml and UseD3D11="0". Done would require a narrowly scoped report or fix with a clearly stated expected result.