mwlwifi falsely supports mesh mode. It exposes the capability to userspace whilst in reality, the binary blob that gets loaded into the 88w8864 flash doesn't support it.
Here is where it gets exposed to mac80211:
Here is where it exposes it's false capability via information element:
This can't be fixed with what's available in the open source "wrapper" of a driver. A lot of the functions are processed in the binary blob which has not been updated since 2016, and it won't be – given that the 88w8864 has been marked obsolete by the current owners of Marvell's wireless business unit, NXP. Perhaps, in the previous pipeline – the 88w8864 and 8894 was going to get proper mesh support at one point, and this was just the groundwork. However, clearly plans have been scrapped with the acquisition that has happened.
Well as you know I spent quite a bit of time with you @jeff and others getting my VLAN system working. I did this so that I could add a second AP using the existing WAN cable. I can confirm that all works lovely now.
I now just need to setup the wireless APs so that clients can freely roam across them. With Mesh 802.11s out of the window I will have a look at B.A.T.M.A.N.
Your wifi device needs to ahve a fixed channel (do not use "auto") otherwise the wireless will not be associated.
But I failed in the next step. My mesh wifi does not seem to have a SSID and therefore it is not shown in the list of wireless networks on my devices. On my Adnroid mobile I found it using "WifiJumper" but it does not have a name/SSID.
Okay. That makes sense. Is there anyway I can test it?
I should mention that I am using a wired backhaul to connect the APs together. Does setting up a mesh add any benefit for better client roaming or am I just better off running dumb APs as I currently am?
Also 802.11s isn't supported on my Linksys WRT1900ACS so the ad-hoc mode is the only other AP mode I can use for setting up mesh.
You generally need at least two compatible routers to test your mesh.
There's no reason to mesh if there is a wired backhaul. Client roaming is a completely different issue than mesh linking. Commercial systems that do both but are advertised as "mesh" confuse this issue.
Unless you have (desktop-) linux clients, none of your smartphones, computers (neither Windows nor MacOS) or IoT/ smarthome appliances can communicate with the mesh itself, they depend on the individual mesh APs to repeat the signal via an ordinary AP interface (and if you look closer, you'll notice in your referenced blog post that they keep the ordinary AP interfaces in place).
The only thing a mesh might improve in terms of roaming issues, is the ability to span a closer -well- mesh of APs throughout the area, so chances for clients to be in range of a strong signal are improved. If you do that traditionally via wired APs or replace the wired backhaul with a dedicated mesh network (which is not seen by your clients) doesn't really matter, but for obvious reasons a wired backhaul will always be faster and more reliable than a mesh.
 unless you expand your mesh beyond property limits and incorporate your neighbours and their internet connections into a common mesh, to gain failover capabilities, but that's a whole difference can of worms