Set up the Flatpak in Desktop Mode, grant only the Steam-library access it needs, and verify a stable profile before moving to Game Mode.
Desktop Mode makes the Flatpak installation, filesystem permissions, logs, and Steam shortcut easier to inspect. Install and open r2modman there first. Do not add it to Game Mode until it can select your game, create a profile, and complete one Start modded launch in Desktop Mode.
When r2modman opens but cannot find a game, Flatpak filesystem isolation is often the relevant layer. Confirm the library path in Steam, then grant access to that specific directory. Avoid opening the entire home directory when a narrower Steam-library permission solves the problem.
Create a clean profile with only the required loader and one lightweight mod. Confirm the game still accepts controller input and returns cleanly to Steam. Keep a vanilla comparison profile so a Game Mode or performance issue can be separated from a loader or mod issue.
After Desktop Mode verification, add the manager to Steam as a non-Steam entry if you want a Game Mode launcher. Game Mode does not replace profile management; it is only another entry point. Return to Desktop Mode for file, permission, or log-based troubleshooting.
A supported Thunderstore community does not guarantee that every package works on SteamOS. Proton prefixes, native-versus-Windows builds, game updates, and anti-cheat rules can all change the outcome. Export a working profile before large updates and test imported modpacks in a copy.
Flatpak is the clearest managed route for Desktop and Game Mode use. AppImage remains a useful portable option for Desktop Mode testing.
Check Flatpak access to the exact Steam library and then verify Settings → Locations. Reinstalling mods will not correct a sandboxed path.
No. The game, loader, package, Proton version, and server rules all affect compatibility.
Research note: September 13, 2026 snapshot. Release assets and platform behavior can change; verify important details again before installation.
Recommended path: read this guide → download or create a minimal profile → record the result → expand to the full modpack.