Normally, I would say Series X from X-Box, just because of its' greater availability and ease of access in the gaming market. But - given your description of yourself being someone coming out of gaming retirement and that you're looking into solo gaming, then I am sorry, but the PS5 wins hands down...

Sony has been known for some of its' stellar solo games. Properties such as Uncharted, Last of Us, God of War, Spider Man are some among the many exclusive properties for the PS5. As a solo gamer, there is no other console that takes solo gaming to the next level like the Playstation. That being said, I said earlier that I am sorry. That's because no one will fault you for not wanting to spend your grandparents' entire inheritance money on a new PS5 console, because that is what it's going to cost you to get one. Moreover with how large these games are, you will need to invest in an SSD drive right from the beginning, which will cost you anywhere from 200 bucks more to...way way more. All in all, once you're done, all of this will set you back a 1000 bucks or close to it.

I am a Sony fan but I refuse to trade my left testicle and kidney to get a game console. Some don't mind, but I do. Because of its' short supply and the current unreal resale price, you're better off taking your chances with the Series X. I personally am just going to wait this storm out to get my PS5.