Should it really require reverse engineering to figure out how a Linux box passes packets?
I gave up on Ubiquiti and bought a tiny $120 router ($140 with a nice metal case) that's a NanoPi R6s. Pretty impressive specifications. 8GB ram, 8 cores (4 fast Ax76 and 4 slow A55s) and no fans. Has 2x2.5GBe and 1x1GBe for networking. I've installed a port of OpenWRT called FriendlyElec and Ubuntu 22.04.1 LTS. I didn't bother cross compiling, it's plenty fast for native compiles.
I've been impressed so far. It compiles Rust about half as fast as my Quad core Xeon server from years ago, and is SEVEN times faster than a RPi 4 8GB! I have an Apple M1 mini around that manages the same compile in 13 minutes. A nice bonus is neither network or storage is USB attached, unlike the RPi.
Burned it in overnight, running all 8 cores flat out, with no problems. Haven't decided what to use, maybe shorewall or just raw nftables/iptables.
Similarly there's 4 and 6 port 2.5 Gbe boxes with various N5000 and N6000 celerons at around $200. ServerTheHome has reviewed many of them, they seem to be evolving nicely, better cases, better heat sinks, better 2.5Gbe Intel chips, etc. Run *WRT, pfsense, or whatever else floats your boat. STH even demod running the firewall under proxmox on one of these cheap 4-6 port 2.5GBe widgets. Would be nice to keep your complete config in git or the config management widget of your choice (often Puppet or Ansible).
Guess I'm just getting less trusting in my old age.