Because FiveM doesn’t link the Steam Overlay as any gameid, taken screenshots don’t appear in the Screenshot Uploader window and you have to go inside Steam to find them. But if FiveM links the overlay as gameid 218, screenshots will appear as Source SDK Base 2007 inside the Screenshot Uploader and they can be easily uploaded and shared.
Also I don’t know if it’s possible, but it would be interesting if screenshots can show the locations where they were taken, example the name of the server, something similar like the image below.
https://partner.steamgames.com/doc/api/ISteamScreenshots#SetLocation
To achieve this I restarted GameOverlayUI.exe with these values
GameOverlayUI.exe -pid GTAProcessPID -steampid SteamPID -manuallyclearframes 0 -gameid 218 -webmicrotxn
and for the Location I added it manually inside screenshots.vdf