OpenWrt is commonly used to breathe new (or better) life into consumer routers, but you can also run it on any x86 machine. I run it on a small, passively-cooled i5 machine* virtualized in Proxmox alongside Home Assistant. I originally ran OPNSense, then VyOS, but eventually went back to OpenWRT since it does everything I want/need with a simple interface.
* https://www.reddit.com/r/homelab/comments/hzvfih/new_router_...