@Kim-Nyholm I think iw and iwinfo are not working as expected due to WARP CORE (the Onion Enhanced MT7688 WiFi Driver).

Check the '/tmp/dhcp.leases' file that lists all the devices which connected to that AP so far (in the last 12 hours - it's the default lease time).
If you want to know only the number of active clients then flush actualize the arp cache in some way.

Do you want an example?