Go to Settings / Sonos (or Sonos S1) and enable Local Network access. This is an annoying new-to-iOS14 setting that is necessary for the Sonos apps to work.

I already did that.

So, is it possible that you have a mesh network, and your controller devices are connected to a different subnet than the speakers are? Try plugging one of the Sonos devices to your router with an Ethernet cable, and unplug any extender devices, and then see if your controller can connect. If that works, there will be next steps, but since controlav’s suggestion would normally have worked in most cases, we’ll need to do some further testing.