Most computers with (at least) two network interfaces will do. If it’s something too crappy your throughput will be limited by CPU speed but I can’t tell you exact recommendations here. Here’s OPNsense’s hardware recommendations for example, they’re not high at all. Off-the-shelf devices that allow you to do this should probably be fine too.

I’d put Linux on it and use nftables but BSD PF seems to be very popular for firewalls (OPNsense/pfSense are built on this) which I have never used so consider that too.