You should be able to see it in your installed apps list. Tells you the version number under the name.

gog is naming files difrently than steam and its confusing

Mine only shows the name, no version number. Same in either grid or list view.

The "View patchnotes" option in Gog's game settings should state the version number of the currently installed version of the game.

———————————————&mdas h;————————————

FYI, @woobgn , the screenshot @darrowlykos provided was not of GOG Galaxy, nor of the GOG site, it was, in fact, of the Windows "Installed Apps". You can check it yourself if you go to Windows -> Settings > Apps > Installed apps.
You can also find the installed version in the legacy Control Panel > Program and Features.
Check the screenshot bellow.

I would also advise you to read the following post, from @HamerUA:
https://www.gog.com/forum/stalker_series/stalker_2_confusing_version_numbers/post5

Here's an excerpt:

1.0 → 1.0.424 (one of initial versions) [2024.11.21]
1.0 → 1.0.436 (possibly a hotfix) [2024.11.22]
1.0.3 → ??? (stays the same)
1.1 → 1.0.669
1.1.3 → 1.0.738

I hope this helps.