Unable to assign MOUSE4 and MOUSE5 keys as Push-to-Talk hotkey

Summary

I usually use MOUSE4 (or MOUSE5) key as push-to-talk hotkey because (a) it is easier than keyboard shortcut because my right hand is always on my mouse and (b) it helps with the gaming as well because the other key (MOUSE5) is assigned to in-game push-to-talk.

Steps to reproduce

1. Go to Settings.
2. Go to Audio/Video.
3. Under Audio, select Push-to-Talk.
4. Click "No keybind set" and try to set MOUSE4 or MOUSE5.
5. See nothing happens.

Environment (optional)

OS: Bazzite (through ArchLinux container)

Logs or screenshots (optional)

In case you do not know what these keys are, see image below: mouse 4 and 5 keys