Possible bad memory controller, whats the recommendation for a replacement these days?

Got a ryzen 5 3600 6-core, pc's being super weird about ram (have 16gigs, pc will \*not\* use more than 6 gigs, running anything ram intensive like tarkov or ready or not throws a bluescreen on finalizing loading. Ordered new ram (64 gigs) and using this as an excuse to upgrade, so I also ordered a new GPU. If I receive the new ram and the issue persists, what cpu would be the logical upgrade without smashing the bank? Havent had cpu really bottlenecking performance but I'm open to some improvement for longevity, and gonna use the old parts (whichever dont turn out to be the problem) to build my wife her first proper pc since she's been trying to game on laptops for a while (struggled through all of elden ring on 25fps). I am forever traumatized about cpus after buying one that didnt fit as a teenager, and seek the advice of people far smarter than I.