After a few years I'm back on OpenWRT with my new GL.iNet GL-MT6000.
I'd like to make it work as an ethernet switch & AP WiFi.
That is, it would be connected to my main router via the wan1 port and all other devices connected to the other ethernet and WiFi ports would follow the same IP provided by my main router. So 192.168.0.xxx
Please describe specifically what you want to accomplish here. Mesh (as a term) is often used incorrectly (not your fault -- it's because of marketing). Therefore, I'd like to understand what you are trying to accomplish (physically as well as functionally).