Forza Horizon 5 won't launch due to installation path too long

**Game information**

Forza Horizon 5 via Proton Experimental

**Distribution name and version where applicable**

Fedora 43 KDE

**Flatpak info**

Flatpak 1.16.2
```
$ flatpak --gl-drivers
default
host
```

**Problem description**

When attempting to launch the game, it fails with the following message:

I know one workaround is to move the game files to a different directory, as described on [protondb here](https://www.protondb.com/users/1282116887). I'm wondering if there is a better/easier workaround though?

**Does this issue reproduce with native Steam**

No, it was working on native steam before

Start by reproducing the Forza Horizon 5 launch failure in Steam Flatpak with Proton Experimental on Fedora 43 KDE, then compare it with the previously working native Steam setup. Investigate the installation-path length constraint and determine whether an easier workaround exists than moving the game files; done means documenting a verified workaround or identifying the limitation.

Written by the indexing model from the issue text.