Returning Gamer: Series S or Series X?

Hi all, returning gamer from the 2010 era. Barely though as I've only really played Halo 1 - 3, Assassin's Creed 1 and 2, and Mass Effect 1.

I'm planning to start paying all the 360 games available on the Microsoft Store that I missed like all the Fable, Gears of War, Red Dead, Dark Souls, Call of Duty, Oblivion, Skyrim etc. Then working my way through the Xbox One games I missed.

Pretty sure it will take me quite a while to catch up. I've started compiling a list and am already up to 260 games. Plus I recently got the Switch 2 and am also playing a bunch of Nintendo games I missed out on.

My question really is, considering my situation, would it be worth it for me to get the Series S or X, especially with the new Xbox coming in the next few years.

Since I'll be starting with older games and working my way up, will I really need the power of the Series X? Would it be better for me to just get the Series S and save the difference towards the next Xbox that comes out (which will hopefully be backwards compatible)?

I only have a 60fps monitor and am not planning to upgrade, so I won't be able to take advantage of 120fps on the Series X.

PS. I'm a Mac user so PC games on Steam isn't really possible for me. I'm open to getting the PS5 but the lack of backwards compatibility with PS3 games is a con for me.

Thanks in advance all.