I'm playing on Steam Deck and can't get the Galaxy overlay to appear. I've downloaded and installed the game via Heroic, offline installer, and through Galaxy. Makes no difference (though installing through Galaxy now properly tracks play time). I've gotten the overlay to work with other GOG games installed through Galaxy, so I know it works on Deck. I'm running the game with DirectX 11 (Vulkan just crashes), as I heard it doesn't work on Vulkan. Removed my --skip-launcher command, in case that affected it. Nothing.

I just wanna see achievement notifications.

so have you got a Larian account synced in?

Yes

I figured it out. You need to launch the game twice (with the Larian Launcher). Launch the game once, get to the title screen. Close out the game (NOT GALAXY), and wait for your playtime to update. Launch the game again, and now the overlay notification should appear during the loading screen. If you're using a controller and your controls aren't working, Al+Tab to Galaxy, then back to the game. BTW, you can close out the Larian Launcher once the overlay is active.