Hi,
Thanks for sharing that issue. I've exactly the same. Took long time to define the issue.
So, on Proxmox 8 at least, when installing pfsense in a standard way without UEFI, we are able to start the firewall and so on. issue is that when restarting on Proxmox 8, pfsense doesn't restart (note that if trying multiple time, seems some of the versions may restart. So, consider it also as a random issue).
Point of attention may be that it is working fine under Proxmox 6. Absolutely no issues with that version.