Hi, I have my network running on a Raspberry Pi 4 with OpenWRT with 3 VLANs, just cable.
Can I add two routers with OpenWRT as APs/Mesh to provide extra LAN ports in other rooms and Wi-Fi access to my VLANs managed in the main router (Raspberry Pi)?
What you're showing is not mesh. It is simply a set of bridged APs. If you've got wires, everything is very simple.
absolutely. Start here:
https://openwrt.org/docs/guide-user/network/wifi/wifiextenders/bridgedap
Adding VLANs is also possible and fairly straight forward, but if you need help we can assist.