Substance Designerr (and any other steam app that needs file system access) can't access fs outside of container

**Game information**
Adobe Substance Designer 2022

**Distribution name and version where applicable**
AlmaLinux 9.1 (Lime Lynx) X11

**Flatpak info**
Flatpak 1.12.7

nvidia-525-85-12
default
host

**Problem description**

I need file system access to open files on my system, but if I do so by adding an override --filesystem=host, I get the bad item warning and steam doesn't start.

**Does this issue reproduce with native Steam**
No, the native Steam has of course file system access. Just let me add a host override :(

Start by reproducing the Flatpak override on AlmaLinux 9.1 with Steam and Adobe Substance Designer 2022, then compare the behavior with native Steam. The payload names no repository files, tests, or entry points; done means the requested filesystem override no longer produces the bad item warning or prevents Steam from starting.

Written by the indexing model from the issue text.