Have you tried the Heroic Games Launcher? It's currently the most advanced launcher for GOG games on Linux, even implementing support for some of GOG Galaxy's online services. Additionally it's officially affiliated with GOG, so you can "donate" to the project by purchasing games through the client.
How did you try to get The Thaumaturge to run? I found that I could run many games on my library without issue using the Heroic Games Launcher, which is arguably the premier Linux client for GOG games.
Turns out you're actually the owner of your home instance. I didn't know that when I made my previous comments.
I'm guessing you're currently paying for your instance's upkeep out of pocket? I can't spot any donation links on your instance. This might work for you personally, but do you really expect other, larger instances to do the same? Even donations are only rarely sustainable.
I hope one day we will find a method to finance websites operating costs without ads.
Never. People don't want to donate, people don't want to pay a subscription fee, people don't want to watch ads. People want everything on the internet for free.
Well-deserved shout-out for GOG. Its standalone installers make actually owning your games much more convenient than it would be on Steam.