I would like to express how bad this experience is every time I want to enjoy one of the games I own on GoG and want to install them on my steam deck using the site’s download version. There are always the same issues:

1. you need to find the correct version to be compatible and run GOG on steam deck , proton GE seams to be working at the moment and not get an error message.
2. secondly, sign in into your account . what a pain . multiple times your correct password is not accepted and you have to go through the most painful captcha of all times.
3. trying to install the game after you managed to log in and have it be stuck at the installation screen forever “allocating space”
4. sometimes at the end of the installation and downloading tenths of gigabytes you might still get an error message.

At the end of the day this needs to be addressed. I have stopped buying GoG games just for this reason. at least let me enjoy the few I have on my main device

thank you

Can I ask you why you think it should be addressed? I assume that when you say "addressed," you mean by GOG: do they claim to support this device in any official capacity; what business is it of theirs to offer a smooth experience on this device?

You don’t need to use Galaxy to download and install games on a Steam Deck.
You don’t need to use Steam to run games on a Steam Deck.
You don’t need to use Proton to run Windows games on a Steam Deck.

I think your main problems come from a bad choice of tools.

If a game works on linux, the gog version also works on steam deck. I have the machine and mostly i play with gog games:

- Install lutris.
- Using gog offline installers linux.
- Installing the game on a windows machine and copying the folder, then use a proton version.
- Use scummvm for that games.
- Retro arch for dosbox core.

It is not so easy that Steam library but there are options.

Are you using the offline installers (Windows versions) of GOG games, or trying to do it somehow through the Galaxy client running on that device? Just asking because you mention "downloading" and "installing" as if they were part of the same process.

Since Steamdeck is basically a Linux PC, does the process of installing GOG games somehow differ from how you do it on other Linux PCs, e.g. via Lutris?

I've been using Heroic Launcher for a while now, and it works virtually flawlessly on my Deck. All my GOG games, almost no hassle whatsoever. It does not. There are better tools available than Galaxy, Heroic Launcher is offically partnered with GOG if that helps. But Lutris is a fine method. To play in Wayland, it is easiest to add the game to Steam as a non-Steam Game so you can run it in gaming mode with the performance enhancements that are available, but this isn't necessary. It's just the easiest way on the device.

As they said - go with Heroic Launcher. It supports cloud saves and achievements.

I also did some magic back in the past to launch GOG galaxy from Steam client directly and then I was installing games from Galaxy. It worked and I had my playtime/save/achievement recorded.

Like paladin181 said , if you want an easy install then play option, you should try Heroic Game Launcher, it's the closest option to Steam with Steam games you can get and they have a partnership with GOG since last year.

Use Heroic launcher.

Tip: When you launch Heroic, go to the "Wine Manager" tab and download Proton-GE-latest, then go to the Settings->Game Defaults and make sure that it's the default WINE version

Tip 2: Sometimes the linux version of a GOG game doesn't work that well compared to running the Windows version through Proton.

True that on Proton part. Proton-GE has also includes additional features and fixes (most notably includes additional video codecs that valve doesn't include for licensing reasons). I've read that there were games that didn't play cutscenes with Proton and those worked well with Proton-GE.