Z790 Pro RS and 4 sticks of ram.

I always recommend 2 higher capacity modules over 4 lower capacity ones. Firstly,
performance is always better on a dual channel setup. Secondly, it's less strenuous
on the Memory controller in the CPU. Considering the IMC (memory controller) is one
of the most common failure points on modern CPUs I always try to keep the load minimal
to get the most out of my CPU's lifespan.

Just make sure your board will support the RAM you get, either on the QVL on it's
product page:
https://www.asrock.com/mb/Intel/Z790%20Pro%20RS/#MemoryRPL

Or on the QVL for the memory itself.