Hello @ThiloteE, noted at https://github.com/ValveSoftware/steam-for-linux/blob/master/RelNotes.md#installation, sharing Steam library folders between OSes is not supported. This falls into the same category of undefined behavior and is a non-starter issue.
Try to copy subfolders of .local\share\steam\steamapps\compatdata from Linux to Windows.
compatdata are the Steam/Proton equivalent of wineprefixes. These dirs contain symlinks named after Windows drives (e.g. c:) where the colon is a reserved character on Windows, as well as reserved names like com1.
Aside from the invalid filenames, backing up Linux files directly to a Windows filesystem is generally a bad idea, because Windows filesystems do not support Linux file ownership and permissions. When you restore the backup from your Windows filesystem back to Linux, some information is lost. In that sense, it cannot be considered a proper "backup". Either backup to a typical Linux filesystem like ext4 or btrfs, or use an intermediate archive like tar to preserve permissions.
syncthing can attempt to preserve ownership on the receiving side, but that means you have to always use syncthing; you can't copy the backup from Windows to Linux without syncthing. I would only use syncthing for simple media (e.g. photos or music) where permissions don't really matter, not for syncing programs or program data which may have complex permissions.
Thanks for the responses and great explanations. I guess this is more complicated than I estimated. Looks like I will just reinstall Steam and download all my games again. I was about to transition from Windows 10 to Linux. After a first installation of Nobara I decided to reinstall and change some partition sizes on this Linux drive, but since I already had downloaded a game in Steam, I thought why not just make a backup, sync that to the Windows drive and then later consolidate all the games from my Windows drive and my Linux drive into one final Steam folder on the Linux drive. The main aim was to avoid having to download ~300GB again, as my current internet throughput is only 16 Megabit/second, which should yield 178,8 GB in 24hours, so overall that will take roughly two days. Not optimal, but fair enough. Maybe I can successfully copy the game data files, but it's probably simpler to just download it all again.
Have a nice day!
WINEPREFIXx1 2026-05
I am not sure, if this is the right place to report my issue, if it is not, please tell me where that would be or please move this issue to the right place. I used the version of Steam that comes pre-installed on Linux Nobara 43.
My system information
Description of my Issue:
I tried to sync a backup of steam data from Nobara to Windows 10 via an app called Syncthing by simply copying the whole
.local\share\steam\folder. Unfortunately the sync failed, because in one of the folders, some filenames contain characters that are not allowed on Windows. I would suggest to rename the files containing special characters. If those special characters are needed, they could be parsed from within a file.Steps for reproducing this issue:
Try to copy subfolders of
.local\share\steam\steamapps\compatdatafrom Linux to Windows.Here are the logs created by Syncthing:
steam sync errors.txt