Sorry for my bed England! JK but English isn't my mother tongue, so please pardon me.

Your system information

• Steam client version (build number or date): Feb 12 2021, 23:22:26
• Distribution (e.g. Ubuntu): Linux Mint 20.1 x86_64
• Opted into Steam client beta: No
• Have you checked for system updates: Yes
• Happens with both kernels: 5.4.0-65 and 5.8.0-43

Please describe your issue in as much detail as possible:

Steam for Linux (installed from mintinstall https://community.linuxmint.com/software/view/steam:i386 ).
Formatted an HDD as exFAT and connected it via USB 3.0. Created a folder in it only for SteamLibrary. On Steam client startup, it says (can be selected, copied)

/media/ugurcan/Ugurcan/Oyun/SteamLibrary has both 'SteamApps' and 'steamapps' directories. This will cause problems. Please fix manually and only keep 'steamapps' 

There is no such folder called SteamApps.

Hidden files are set to be shown.

I tried renaming folders, searching for SteamApps on my system, creating a new folder in same drive, but none of them worked. Also, using client after this warning pop-up, downloading games and launching games are OK. When I plug same HDD on Windows and launch Steam client, it doesn't say anything, it just works there too.

Steps for reproducing this issue:

1. Format an HDD exFAT
2. Open Steam client settings, choose download location and create folder in it
3. Click OK.
4. Quit Steam.
5. Launch Steam client.
6. Warning pops up.
7. Repeat 4.