APuP (Access Point Micro Peering) is experimental so far. From the patches:
A simpler and more useful successor to Ad Hoc, Wireless Distribution System, 802.11s mesh mode, Multi-AP and EasyMesh.
Almost plain APs communicate between them via 4-address mode, like in WDS but all of them are AP, so they can eventually communicate also with plain stations and more AP nodes in sight. Low hardware requirements, just AP mode support 4-address mode, and no more unnecessary complications, like hardcoded bridging or routing algorithm in WiFi stack. For each AP in sight an interface is created, and then it can be used as convenient in each case, bridging, routing etc.
- OpenWrt merge request: https://github.com/openwrt/openwrt/pull/15442
- Radio interview with the developer: https://radio.freifunk.net/2023/06/13/mesh-in-ap-mode/
I hope that helps 
It is cool that you can use this to mesh via AP only and without modifying the Linux Kernel.
EDIT: I has been merged to master!
EDIT2: A blog article: https://blog.freifunk.net/2024/08/24/a-new-way-to-mesh-apup/