I'm not sure future proofing with AM4 is really possible, we may be at the end of the sockets life with the Zen3 chips. AMD promised support through to this year when it released, there is no guarantee there will ever be an upgrade past Zen3 without a new socket. It's been a pretty good run so far.
I have an X470 board and a Ryzen 2700X from 2 years ago, I may put a Ryzen 4xxx into it at some point and if I do it'll be the first time I've ever kept a motherboard from a gaming PC and done a CPU upgrade. People talk about future proofing a lot but by the time a PC is 2-3 years old it's generally easier to replace MB/CPU/RAM all together and sell the old ones as a set. Any older than that and it becomes almost the only way.
My personal advice is just built the PC you want now and don't concern yourself with "future proofing"