I found an old 3u server chassis and put a regular atx motherboard power supply in it. 4 noctua 80mm fans and it’s relatively quiet for a server.

I bought one of those passively cooled router boxes from AliExpress and have been running opnsense for over a year on it now. It’s way overkill for router + ad blocking, but it’s been working great.

I did this for a while, but decided to just run opnsense on bare metal, I didn’t want my whole network going down if I had to restart Proxmox or something. It’s way overkill but it’s running opnsense, adguard and will soon be running ngnix hopefully.