Your system information

• Steam client version:
• Distribution: Arch Linux and SteamOS
• Opted into Steam client beta?: Yes
• Have you checked for system updates?: Yes
• Steam Logs: steam-logs.tar.gz
• GPU: AMD

Please describe your issue in as much detail as possible:

Demonstrative video: https://youtu.be/HD8XqY07uUE
If I try to use the "Show on disk" option in the Screenshot Manager with system or non-Steam game screenshots, nothing happens. The option works perfectly fine for any official Steam game.
I have tested this on both Arch Linux and SteamOS

Steps for reproducing this issue:

1. Open Screenshot Manager
2. Select a screenshot of the system or of a non-Steam game
3. Try to use the "Show on disk" option

Results

Nothing happens

Expected

The location of the screenshot should open in a file browser