DDR4 Vs DDR5 (dad has lots of spare DDR4)

My dad has lots of spare 16 and 32gb DDR4 sticks laying around in his lab. (is a research professor and was getting a bunch of ebay computers and swapping parts around) Would these be useful for a new build? How does ddr4 vs ddr5 compatibility work?

I was looking at something like the pcpartpicker "great AMD gaming build" or "excellent AMD gaming build" with a ryzen 5 7600x or 9600x and a RTX 5070. It seems the suggested motherboards and CPUs for that don't support DDR4.

What CPU and motherboard should I use then? Or should I just bite the bullet and get DDR5. I can afford it.