At the end, I put back version 3.12.2 MK3S+ and 1.0.6 MMU2S and the printer/mmu works fine now. There is something in 3.13.0/3.0.0 that makes the MMU fail to home the idler. So I will stay one version behind for now until someone with more skills and patience fix this issue which seems to be affecting other users as well.