Difference between RetroArch for PC, Steam or XBOX??

Sorry, I'm new to this community. I'm sure the docs have this information but haven't found it, so I come here.

What's the difference between retroarch for xbox series and pc?? Besides specifications, are there cores I can't run on both versions? Or games I can't run in both versions??

Is there a difference between PC direct windows version and Steam version?? I know that in steam version I have to download the cores individually, but I have the same questions: are there cores I can't run on both versions? (maybe cores not available) Or games I can't run in both versions??

The thing is I have a modest PC, and I was considering buying an xbox series for the emulation (besides xbox games), but if there is not much any difference, maybe I will skip the xbox.