Main router: Redmi AX6000 (23.05-rc2)
Secondary router: Redmi AX6S (22.03.5)
Both of them have wpad-openssl and mesh11sd installed. The second router's br-lan is configured to be a DHCP client. Both router can connect each other using 802.11s, however the host field in list does not have any IP addresses and there's no internet access if I connect via AX6S.
So we can get an idea what is going in, on your "Main" router, show the outputs of:
uci export network
uci export wireless
Paste the outputs into the text box one at a time, highlight the block of test and click the </> on the top menu of the test box so we can see the text properly.
Okay, since I only have two routers, I'm using WDS now, it works just fine and speed is decent.