Theoretically there's no reason why this shouldn't work, but you likely will find the software isn't designed for multi-GPU and have to reimplement/fix things y

Theoretically there's no reason why this shouldn't work, but you likely will find the software isn't designed for multi-GPU and have to reimplement/fix things yourself. You will also be getting about 720GB/s of memory bandwidth with 2x3060; instead of 1TB/s with the 4090; so expect lower performance.