Linux: Bridge an AP to a mesh node

Hello all and thanks in advance for your help!

I have an existing mesh-network, configured on a router running OpenWRT. AP on 5G, Mesh-communication on 2,4GHz.

A Raspberry Pi running Raspbian is connected to the mesh on an external wifi-adapter.
Now, I want the onboard wifi to act as an AP and emit/expand the mesh/internet.

Question: How do I bridge the existing mesh-connection to an AP? All of the tutorials that I found, create an AP that assigns IP-Adresses (which in my case shouldn't be done because the OpenWRT Router handles them).