Just installed Proxmox 7-1-2 on a Poweredge r410 and I have tried multipole fixes and I cannot access the web interface. Just ran ip -br -c a and got that vmbro0 DOWN 192.168.1.174/24
Change cables, change ports, try direct connecting other devices, move cable to eno2, change NIC, try different kernel, try vanilla debian ISO.
if you tried all of the above and there was no change in port state and you never transitioned from "no carrier", then perhaps you have a bad motherboard or extremely high electromagnetic interference and next call might be to EPA.Im trying all that now and no change.