just out of curiosity - how would You go about that link of the 3 cards? Does AMD have anything like NVLink? (honest question, I really don't know and suspect I might have missed a bit somewhere in the idea)
nvidia dropped nvlink from their consumer cards, so for the consumer nvidia and amd cards it would work the same - trough PCIE
Through pcie using GPU P2P with a supported AMD chipset (epyc processor) so they can talk to each other or going through your CPU and RAM. I think the latter is what people using nvidia RTX 4090s do because P2P is disabled and NVlink is unsupported