The neighbour definitely has problems with his wifi as well, so fixing the issue would be beneficial for everyone. Step 1 would be to use APs that are connecte

The neighbour definitely has problems with his wifi as well, so fixing the issue would be beneficial for everyone. Step 1 would be to use APs that are connected with ethernet instead of Mesh-type APs. That would greatly reduce the amount of data that needs to be transmitted (with mesh, your signal needs to be repeated multiple times. With ethernet it's just transmitted once) Step 2 would be adjusting power output of each AP. If the neighbour has multiple APs, they probably don't each need to run on full power. Step 3 would be looking for devices that transmit a lot of data. I assume most of the 120 devices don't cause a lot of traffic. Maybe there's just a few that cause 90% of the traffic. Maybe the most traffic intensive devices (eg. camera) could be replaced with a wired connection. I'm assuming the neighbour doesn't know anything about how to optimize Wifi networks, but OP sounds knowledgable, so maybe they could work together to fix the issue. It can be a Win-Win situation: OP gets a usable 2.4GHz channel, Neighbour also gets better connectivity.