I purchased a firewall appliance with 4 ports and installed opnsense on it. Best decision of my self-hosted life.
Get one with two 10gbps ports and you are set. Passive cooled, small factor, Intel atom CPU. 4gb ram is plentiful.
On aliexpress can be found for 100€ or little more.
Even much better than an OpenWRT, which I love and use but delegate to internal network (WiFi access points) rather than perimetral defense.
My family has a junk home, not just a drawer :)