Heroic Games Launcher v2.12.0 brings lots of improvements and some fun experiments
gamingonlinux.com
I personally LOVE Heroic Games Launcher. I have GOG, Epic and Amazon all in there, though I VERY rarely actually play any games from them. But haven't had an issue with the games installed from it yet.
If you like Diablo, try NoX. I think it's only on GoG but I could be wrong. There is a fan patch in the comments there to get it all working 100%.
It's also on Origin but why buy there when you can buy on GOG.