OPNsense works fine under proxmox, I use it that way a lot, including for OPNsense code development.
I've done a video on how to install OPNsense on Proxmox, if it helps:
https://youtu.be/-eqenlbBDLQ
I've done a video on how to install OPNsense on Proxmox, if it helps:
https://youtu.be/-eqenlbBDLQ