you don't have enough lanes to run 3 videocards unless one is though usb 3.2 / thunderbolt on a external.
You need a HEDT.
Intel is the cheapest at the moment with pci-e 5.0.
3435x
2455X
The complete board and cpu will net around 2400 / 1900 dollars. You will need 8 sticks of ddr5 ram tho on the top link, unless you decide to go on the cpu to a 2400 series which i would say do a HARD pass on, as you lose PCI-E lanes on a 3400 vs 2400.
However if your looking for the cheapest to support 3 video cards its the 2455X.
AMD TRPro's (Stormpeak) are just right around the corner, but no one has pricing on them yet, or if you can get the lower end cpu's without going though a SI.
The upper end TRPro and Xeon's expect to pay 5-6k just on the cpu, which isn't really worth it, unless you do heavy content creation / professional stuff that isn't quite yet on the level as full enterprise.
I understand OP is on AM5, I could have sworn that those had bifurcation. I could be wrong of course.
I don't think many will because only the first slot is a physical 16x.
Unless they decided to Bifur the second 8x slot into 2 x 4x.
EDIT:
PCIE bifurcation on ASRock Lightning PG X670E
PCIE bifurcation on ASRock X670E Taichi
So i guess the X670E's have them.
Typically i don't think the first slot which is always the dedicated gpu slot, would ever have bifur without bios mod on a consumer grade board that is non HEDT.
There might be some other enterprise class X670 that MIGHT have it as well, like ones from ASRack, or Supermicro.
But im not too familiar with that line of boards.