Offloading the Snort work to another device

I have a router with about 500mb ram, I want to run Snort NIDS on the network, however the wiki for SNORT on Openwrt states

SNORT takes an absurd amount of memory and processing power with rules, BEWARE. Some people choose to offload the work to another device!!!

When I search how to do this on OpenWRT it says that version 2019 should have a port mirroring feature built in to the system under Network -> Switch

Before version 2019 port mirroring should be acheived by installing an iptables extension.

The only problem is that on version 2021 of OpenWRT the Network -> Switch does not exist, and I cannot find anything in the Lucy about mirroring, and I am unsure if I should just install the old extension that was used before 2019.

When they say offloading they mean get a dedicated device like a computer or virtual machine with two network adapters and run snort on that not openwrt