Obviously... don't be on 7/8 -.-
https://help.steampowered.com/en/faqs/view/4784-4F2B-1321-800A




Yes, R* removed support for windows 7/8 -
https://support.rockstargames.com/articles/21494223343379/End-of-support-for-Windows-7-and-Windows-8-in-the-Rockstar-Games-Launcher-and-on-supported-Rockstar-Games

but wait wait!! - I am on windows 10 or 11! ---- keep reading.

https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=3209461903
(this problem can also appear as initialization errors)
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=3228911640
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=3228912515

You may even see this in my docs / rockstar games / launcher / launcher..log =
[2024-04-30 09:11:36.610] [ ERROR ] [Main ] [error] * Code: 111 (LAUNCHER_ERR_UNSUPPORTED_WINDOWS_VERSION)
[2024-04-30 09:11:36.610] [ ERROR ] [Main ] [error] * Extra:
[2024-04-30 09:11:36.610] [ ERROR ] [Main ] [error] * Localised: Only Windows 10 and later are supported. Please verify your OS version and check your Windows compatibility settings by right-clicking the game icon and going to Properties->Compatibility."

Onward to fix-
Rightclick gtav(or rdr2) in steam, properties, installed files, browse installed files.
Rightclick each application / .exe in there (gta5, gtavlauncher, playgtav, or rdr2.exe and playrdr2.exe) -
properties, compatibility tab - uncheck windows compatibility mode, apply.
(yes, you can 'run' gta5.exe as other compats for 'reasons' - sort it out yourself)

If you are on EGS or R* versions - the same may very well apply.
Go remove windows vista, 7, 8, 8.1 compatibility mode enables. -.-

Then go to c / program files / rockstar games / launcher -
(or wherever you installed if not default - rightclick shortcut, open file location)
Remove compatibility mode on r* launcher.exe, / launcherpatcher.exe (check other .exe if you want).

edit - and removing compatibility mode on the steam.exe as well / restart steam~

Test. If it doesn't work - make sure that the launcher has closed out completely - force close it in taskmanager or restart pc if necessary, and try again. There have been apps over the years that have prevented proper game/launcher shut down - ghub is one of them.

If you have multiple folders/copies installed - be sure you've checked them all.

Some users claim 'run as admin' is also triggering this - but I've not tested/seen. I'd imagine you'd have to test 'that' across steam, r* launcher exe's, social club exe's, gta5.exe's. Again, not testing that. The only 2 things triggering the compatibility box -for me- are - R* launcher, and launcherpatcher (I'm on win10). Win11 users may see different behavior.

It may be possible that users 'NOW' require RUN AS ADMIN to be checked for launcher, or launcherpatcher. The R* launcher/files, and gta5/rdr2 .exe's - have been rife with issues of run as admin or not varying across systems, windows versions, builds - for years. Be methodical and test it all.

Said differently -
https://gtm.steamproxy.vip/app/271590/discussions/0/4205868123784152389/#c4205868123784172359

/goodluck

edit - This doesn't account for any newly created R* errors/causes. Some users claiming to need to manually install battleye for this to work but I've not experienced this yet. Isn't hard to do - just got run gta5_BE and it should install. There is also a battleye folder with a .ini you can edit to make it not silent, etc. Either way, easy enough to test. Beyond that you get into vcredists, antivirus/securiy etc (including things that possible mess with battleye but I digress). You could also just opent he R* launcher, and disable battleye to remove that part of the equation via settings - uncheck battleye. I mean, when I uninstall battleye here - it doesn't give that error.. anyway. I think it had more to do with a pc restart, and the closing/restarting of apps after having checkmarks removed. But just IMHO~