After some fiddling in the first week I never really cared about getting my gog games to my Deck - but now for that I'd be interested what's the best option to install, keep up to date and sync my saves?
Definitely Heroic Launcher. It will do everything you want for your gog, epic and amazon games. Cloud saves are still an experimental feature (afaik) though. Oh, and updating isn't automatic. You'll have to update by going into desktop mode, starting heroic launcher and update your game from there.
Here's the advice I found somewhere else, it looks really good now:
I'm running a few lows and mediums, but the most important are textures at medium or high, models on medium and low, FSR on Ultra Quality and AA on the far option. The image quality becomes acceptable and it runs at 30 fps with ocasional dips.
I'm finally playing thru the Witcher 3 (always stopped at like 10hrs before, currently 22hrs in) but as soon as I'm done with it I'm buying this game. Can't wait plus we should all be supporting a game with no microtransactions