Object detection will be a challenge, especially for multiple cameras. It’ll probably be fine if you have an Intel processor with quick sync.
I’m running Blue Iris on a Windows VM. I also have codeproject.ai on an Ubuntu VM with a Quadro P2000 for object detection (it also does Plex transcoding, the object detection doesn’t stress it very much).
My previous “home server” was a raspberry pi 4 running home assistant and motioneye for 2 cameras. It was able to handle it with a reasonable amount of headroom. That being said, I couldn’t imagine an SBC being able to handle object detection on top of that.
HARDWARE:
PROXMOX: