I was having this issue. It looks like it's an issue with the desktop launcher file not launching steam correctly due to the system not using the correct GPU on NVIDIA prime systems. I found that there is a defunct steam running on my system already by launching it with the desktop launcher file.
Find the process: ps aux | grep steam
$USER 115599 0.0 0.0 10232 3800 ? S 14:53 0:00 bash $HOME/.steam/debian-installation/steam.sh -nominidumps -nobreakpad
$USER 115746 0.1 0.0 0 0 ? Zl 14:53 0:00 [steam] <defunct>
$USER 116535 0.0 0.0 9076 2204 pts/1 S+ 14:56 0:00 grep --color=auto steam
Kill the process: kill -9 115746
Run steam again via the command line and it should launch this time around : steam
After that, modify your steam desktop launcher file at /usr/share/applications/steam.desktop
change line 38 from
PrefersNonDefaultGPU=true
to PrefersNonDefaultGPU=false
This requires root privileges, if you don't have root privileges you should be able to use steam via the command line.
Reboot and the steam desktop launcher should work.