I have switched from PS to Xbox in the PS3 gen and I would say that I not regret it. It is true that Sony exclusives won't be on Xbox, but you win other advantages like its fenomenal retro and a library that your spouse didn't play before.

In my case, I really like the hardware, it's really solid and with the Gamepass he will play lots of titles that otherwise he will not play. But, I will mention that lastly I feel a bit concerned about the release planning of the Xbox division...

It's up to you, but in case you want to not mistake in the decision, instead of going for a Series X, my sugestion is going for a Series S, which is more affordable and all actual videogames can be played there. Once the PS5 offer stabilizes, then he can thing whether is a good idea to go for a Series X or a PS5. But in the meantime, he can play everything :)