The Switch UI is very similar to the PS4 UI (has horizontal scrolling list, separate main library - Sony's added more things since first launch but for the most part the Switch UI and PS4 UI are very similar to each other). The only thing that is different is the UI styling - Nintendo went with flat UI (flat shapes, flat colors meaning no gradients etc) vs Sony who didn't go flat, they're using translucency/gradients etc.
I think PS5's will be similar to the UI of the PS5 with some enhancements. Some people here sure like to over-react on things. Look and feel while important will not over rule if the UI is easy and straightforward to use.
I've been doing some serious thinking about the PS5 and the UI. During that time I kicked a can, skipped some rocks, talked to strangers, took candy from said strangers, had some quiet time in the woods, gave someone a front wedgie, took a stroll through a dark alley, pocket dialed people for fun, gave kids bad advice, had a drive by argument, left an IOU in a donation box, picked up a hitch hiker, gave strangers a soggy handshake, taught a ghost to break dance
way, and had some black-guy thinking time. I've come to the conclusion that I cannot in good conscience get a PS5 when the UI is so butt ugly. Sure you only spend like a minute looking at the UI, but that is a minute too long. You broke my heart Sony.
UI no need to be pretty or flashy. what important is its working, easier to read/understand, user friendly, easier to navigate and doesnt lack of features. thats why, current modern trend is simple is better.