4k monitor or full hd?

I have to buy a new monitor these days and don't know exactly whether 4k is worth it for me.

My PC: geforce 1060 3gb, Intel i7 6700.16gb RAM

I realize that I can't play the brand new games on 4k, but maybe the old ones? And is the qualited of full hd worse on a 4k screen than on a full hd?

Because if I already buy I want to buy it for the future, for example if I want a ps5 or something similar.

And do you have specific recommendations?

How much money do you want to spend?
all the new technologies e.g. Hardly in 4k
at 1440p it is sometimes reasonably affordable, while fhd offers a good mix of office and gaming

About 500 euro

https://geizhals.de/...&bl1_id=30