TLDR: Just scroll down to The solution.
Today (2024-03-09) I tried to run Counter-Strike Source on Void Linux via the Flatpak version of Steam on Void Linux. I have updated all my Flatpaks via flatpak update before I started Steam.
After trying to run Counter-Strike Source, it just stopped. No game window opened. The green Play button of the game just updated to the blue Stop button and eventually reverted back to the green Play button.
So I ran Steam via the console using flatpak run com.valvesoftware.Steam to look at the logs. The game had problems with line 72 of hl2.sh, printing
/hl2.sh: line 72: Aborted