Iirc classic WRT-841 and similar "300Mbit WiFi" generation 4-100Mbit-ports Wi-Fi routers had the CPU attached via an on-SoC gigabit link to a vlan capable switch that has the 4 100BASE-TX ports exposed.
I guess it's cheaper than having to redesign an entire SoC, but still...
Mikrotik makes block diagrams of some of their Routerboards available. This is a hAP AC3, for example
https://i.mt.lv/cdn/product_files/RBD53iG-5HacD2HnD_201031.p...
It runs on a Qualcom IPQ4019 single-chip Wi-Fi system-on-chip (SoC)