Left4Dead2: Any mods that change visuals in the game (Models, Textures, e.t.c.) do not work

**Game information**
Left4Dead2

**Distribution name and version where applicable**

Operating System: openSUSE Tumbleweed 20211220
KDE Plasma Version: 5.23.4
KDE Frameworks Version: 5.89.0
Qt Version: 5.15.2
Kernel Version: 5.15.10-1.g85804f3-default (64-bit)
Graphics Platform: X11
Processors: 12 × AMD Ryzen 5 4600H with Radeon Graphics
Memory: 7.1 GiB of RAM
Graphics Processor: NVIDIA GeForce GTX 1650 Ti/PCIe/SSE2

**Flatpak info**

Flatpak 1.12.2
nvidia-470-86
default
host

**Problem description**

Some addons on Steam Workshop does not work, but in native Steam install, it work.
When installing addons from Workshop, the addons does not take any effect.
However, certain addons work, maps does work.
Example of addons from Workshop that does not work.
[
(https://steamcommunity.com/sharedfiles/filedetails/?id=2391317018&searchtext=%E6%9C%89%E6%A0%96%E3%83%9E%E3%83%8ASpas)](https://steamcommunity.com/sharedfiles/filedetails/?id=2391317018&searchtext=%E6%9C%89%E6%A0%96%E3%83%9E%E3%83%8ASpas)

https://steamcommunity.com/sharedfiles/filedetails/?id=1668705398

https://steamcommunity.com/sharedfiles/filedetails/?id=2241027900

**Does this issue reproduce with native Steam**

No, native Steam work.

Start by reproducing the listed Left 4 Dead 2 Workshop visual-addon failures in the Flatpak Steam package and compare them with native Steam, using the provided addon links. Done means determining why model and texture addons are ignored while maps work, then documenting or correcting the Flatpak-specific behavior and verifying those examples.

Written by the indexing model from the issue text.