Hello @dtantono, managing select-able Steam Play compatibility tools is handled by the Steam client, not Proton itself, so I've transferred this issue report.
@kisak-valve yeah, my Ubuntu PC can detect newest proton 8.0. But, SteamOS cannot which is weird.
I have the same problem. Not display in list view steam os proton 8.
proton 8.0x2 2023-04
Hi
I install the proton 8.0 (the directory is /home/deck/.local/share/Steam/steamapps/common/Proton 8.0/) by Desktop mode > Steam > In Library select "All" and "Tools" > Search for Proton 8.0 > Install. and it didn't show up on Steam (Setting -> Steam Play). even after reboot. what do you think?

PS: it shows up on Heroic BTW