Okay, solved, I removed the Unifying Receiver, then I unpaired/repaired my BT device. Now it is working, but it forgot all my previous settings. :( Too bad, but at least it is working via BT again.

I'd like to add some further details to the issue:

My mouse was paired via Bluetooth, but after the last update of the Logi Options+ app, it stopped detecting the device - while the OS detects and uses the mouse without any problems.

Then I tried to use the Unifying Receiver and this way I was able to have my mouse detected by the Options+ app, and I was also able to configure it.

But I would prefer the Bluetooth connection instead.

Thanks.