Please make sure to have Overlay enabled both for the platform and GWENT itself.
GOG Galaxy: go to Settings in GOG Galaxy -> Game features -> In-game features -> Enable Overlay.
In order to enable Overlay for GWENT, right click on GWENT in the GOG library -> Manage installation -> Configure... -> Access GOG Galaxy features in-game.
Steam: go to Settings in Steam -> In-Game -> Enable the Steam Overlay while in-game
In order to enable Overlay for GWENT, right click on GWENT in Steam library -> Properties -> General -> mark "Enable the Steam overlay while in-game"
If this does not resolve the issue, try the following: