I installed Proxmox and then OPNsense. Everything seems to be working fine until I click on almost any option of the web GUI- Update, Lobby Section: Dashboard, Unbound section: Log File, System Section: Firmware, etc.
I get a small popup box that says DANGER, and then Unexpected Error, check log for details. However, I can't see any. Once I'm done closing out all the popups, the Dashboard page is completely empty. If I try clicking it, I get the popups again.
Well, I discovered the issue.
Ublock Origin specifically on the Brave browser. I also have the Extension running on Microsoft Edge and it causes no problems. Just in case this helps someone in the future.