I also switched to Pop!OS recently!
Cannot add library in Steam
I had the same issue. You likely installed Steam from the Pop! Shop by selecting "flathub (flatpak)" which I believe is the default option. You won't be able to access other drives because of the way flatpaks are containerized (or something along those lines). Go back to the Pop! Shop, uninstall Steam, and then reinstall ofter selecting "Pop!_OS (deb)" from the drop-down menu just below the name of the program. This version isn't containerized and can access your other drive. Edit: Another thing! When you reboot your system you might need to remind Steam to have another drive. For whatever reason I need to go back to "add drive" and select the drive before Steam remembers that's where all my games are installed.
crackling and audio cutting out
I haven't had this exact issue but I did need to play around with PulseAudio/PipeWire to get my microphone to work. I remember uninstalling and reinstalling stuff related to PipeWire and then rebooting the system and my microphone worked.