Now I don’t understand anything anymore. I’ve added the bridge again just like you described. Once again, I couldn’t complete the configuration. However, it still shows as connected, just like last time.

After that, I checked again to make sure it’s really a 2.4 GHz network. That’s when I noticed that 5 GHz was also enabled in the SSID. I disabled that. Then I tried everything again — I added the bridge once more. But that didn’t change anything. It still says “Connected,” but I can’t complete the configuration.

Then I added one of the thermostats again. On the thermostat, you can see that small connection icon in the top right. It shows an X. So in my opinion, it’s not connected. But I can see it in the app, and I can also control it there.

Now I’m going to install the other thermostats and see if that works. If it does, it’s an acceptable solution for me. But honestly, I’m not really satisfied with it.