A game on an exFAT drive will not start, and Valve says Proton cannot support it
A Steam game installed on an exFAT drive can refuse to start with nothing on screen to say why, and Valve has now given the reason in one sentence: "Proton currently can't support exFAT due to missing filesystem features." A Valve member wrote that on October 16, two and a half hours after the report that prompted it, and closed the report as a duplicate.
The demo for Rhythm Animal Café is the game that would not launch from the exFAT drive, four days after the full game reached Steam. Image: Salt Game Studio
The symptom is the part an owner meets first, and it is silence. The report describes a library at /mnt/nvmeexfat/SteamLibrary on Arch Linux and a game that "shows it's starting but then it goes back to 'start game', silently. Nothing launches." No dialog, no error, no log pushed in front of anyone.
The game was the demo for Rhythm Animal Café, a Salt Game Studio rhythm game published by XD that reached Steam on October 12. The reporter tried Proton Experimental, GE-Proton and a third community build before filing, which is the obvious move and the wrong one here, because the compatibility tool was never the variable.
Proton stops while it builds the Windows prefix
The log in the report points at one step. Proton gets as far as upgrading the game's Windows prefix and then stops on a symbolic link it is not allowed to create, with "Operation not permitted" against a file it is copying into the prefix.
That is early enough that the game never runs a frame, and late enough that Steam has already shown the Play button going green. Moving the library to an ext4 drive fixed it, and that is the only remedy in the report.
Nothing in the fault belongs to the game, which runs once its files sit on an ext4 drive instead. Image: Salt Game Studio
Valve has tracked exFAT support since May 2020
Valve pointed at the item it tracks this under, and it is not new. The exFAT support request on the Proton tracker was opened on May 6, 2020, has 12 comments, was last touched on November 14, 2025, and is still open and still labelled a feature request.
The request names the obstacle in concrete terms. Wine keeps a dosdevices directory whose filenames contain a colon, which exFAT does not allow, so a game's compatdata directory cannot live on an exFAT partition at all unless a symbolic link sends it somewhere else.
Valve's word is "currently", and nothing in the reply sets a version, a date or an intention. It closed the report as a duplicate rather than answering it, as it did with a Half-Life: Alyx crash whose duplicate trail ran back to 2020.
Salt Game Studio developed the game and XD published it on October 12, listed for Windows, which is why it runs through Proton on Linux. Image: Salt Game Studio
The report asked for a warning, not for exFAT support
It asked Steam to tell an owner when a launch fails this way instead of failing quietly, which is the difference between a five-minute fix and an evening of swapping Proton builds.
Valve's reply names that one too. A second report, open since November 30, 2021 with 23 comments, asks Steam to warn before it launches a game from a drive that is not ext4, on the grounds that those launches are almost certain to fail.
A warning of a different kind did arrive this month, when the October 13 client started telling desktop Linux owners that a game is known not to work with Proton. For an owner who formats an external drive or a card so Windows can read it too, the one working answer is still the one the reporter worked out alone: put the Steam library somewhere else. The warning the report asked for has been on Valve's tracker for nearly five years.
