Sorry if this has been asked multiple times before which im sure it has. I have searched but so far cannot find a recent discussion. Please feel free to refer me to any previously answered discussions rather than repeat what has been answered before if you so wish.

Before purchasing a game, what is the main thing to look for to know it is 100% compatible to play via Nvidia GFN.

I'm currently without console or PC so I cannot link my steam for cloud gaming on the steam app or xbox app leaving me with only GFN as a last resort.
However, when I sync my steam on GFN only some of the games in my steam library show up/ are playable, even after purchasing a game and re-syncing the two.
I'm not the most technical minded however I would appreciate if someone could explain what I'm missing before I purchase any more games that I current won't be able to play in my situation.

I'm confident that my S24 ultra is capable to stream play games from various sources on GFN because it handles things like Euro truck sim with in game mods, on high res without any issues.

Thank you in advance if you can point out the obvious mistakes that I cannot.

And apologies if this has been answered before.