I have 2 Pi 4s in operation. One is a Moonlight/USBoverIP stream gaming portal. It automatically turns on and connects to a VM running Sunshine on my Proxmox host, passes any USB controllers/bluetooth etc to the VM so the big loud gaming box is in the basement and the tiny Pi is next to the TV. 1080p60 works great, minimal lag.

The other acts mostly as a quorum server for the proxmox servers, I have two proxmox hosts and use the second Pi to ensure the cluster doesn’t get split brain. It also acts as a USBoverIP host for my home automation Zigbee and Zwave usb sticks, so that either proxmox host can connect to the USB sticks and the home automation VMs aren’t locked to a physical host.