Your system information

Steam Version: 1687015240(Latest Beta)
Steam Client Build Date: Sat, Jun 17 10:53 AM UTC -05:00
Steam Web Build Date: Fri, Jun 16 8:51 PM UTC -05:00
Steam API Version: SteamClient020
Distro: Endeavour OS(arch)
Window-Manager: i3
Any modifications above distro?: Only changed fstab for mounting external drive and I have lutris installed which installs xdg-desktop-portal-gtk
Opted into Steam client beta?: Yes
Have you checked for system updates?: Yes
I trimmed logs for you:
When I click Add Library for External Drive, it says nothing, but the console says something:

ExecuteSteamURL: "steam://open/steam://settings/"
Couldn't write /boot/efi/.steam_exec_test.sh: Permission denied
Couldn't write /media/sd/.steam_exec_test.sh: Permission denied

(steam:32336): GLib-CRITICAL **: 07:51:01.525: g_main_context_push_thread_default: assertion 'acquired_context' failed

(steam:32336): GLib-CRITICAL **: 07:51:01.525: g_main_context_pop_thread_default: assertion 'g_queue_peek_head (stack) == context' failed

Steam runtime diag: https://gist.github.com/EndChapter/9208da6f638632f488e087fc1fc077eb
GPU: Nvidia/Intel

Please describe your issue in as much detail as possible:

Cant add external drive as a library and cant install games because of that rn. I have 120gb ssd and I cant install certain games into the ssd. I need that external 1tb storage but I cant add new steam library. It looks like it is an UI problem.

I tried to add them to libraryfolders.vdf as a workaround, but it doesn't work.

Edit: For people facing the same issue: As a workaround, I opened Steam Console via steam steam://open/console and then added a library with library_folder_add <path>.

I checked for other issues. I don't have xdg-desktop-portal-gnome.
pacman Query results:

pacman -Q | grep gnome
gnome-desktop 1:44.0-1
gnome-desktop-common 1:44.0-1
libgnomekbd 1:3.28.1-1
polkit-gnome 0.105-10

Also, Steam should not try to write to the EFI folder. when adding libraries.

Steps for reproducing this issue:

1. Create external hdd drive
2. Mount it via fstab(to the /media/something)
3. Try to add library via steam.

Edit: I tried with full disk access. It seems It doesn't related to full disk access

Edit 2: System information

Edit 3: Steam runtime diag