No, you do not need an additional Bluetooth receiver for the keyboard if you are already using a Logitech Unifying USB Receiver from a Logitech mouse. The Logitech Unifying USB Receiver can connect multiple compatible devices, including the MX Keys keyboard, at the same time. You can therefore connect the keyboard via the existing receiver. Alternatively, you can also connect the keyboard via Bluetooth if your iMac supports Bluetooth Low Energy.
https://support.apple.com/de-ch/102646#:~:text=Bildschirmfotos%20auf%20dem%20Mac%20aufnehmen,%3A%20Umschalttaste%2C%20Befehlstaste%20und%203.
That's not how it works?
The setting Keyboard language Switzerland, German works correctly for me. However, I have been uninstalling Logitech Options for some time because it does more harm than good. Try it without Logitech Options.
The dongle is optional, but it is not a Bluetooth dongle, but a stand-alone connection method from Logitech.
You can therefore use the keyboard either without a dongle (Bluetooth required) or with a dongle (no Bluetooth required).
Unfortunately, there hasn't been a silver version produced by Logitech for the "full" keyboard. The only alternative would be this mini-keyboard without the numpad: Logitech MX Keys Mini for Mac (CH, Kabellos)
There is no information about this. However, I suspect that the keyboard will not be very loud as they use a dome-switch keyboard. In most cases, a plastic dome that is pressed in by finger pressure and hits the circuit. Most keyboards available today use dome-switch technology.
i use the keyboard with a mac, it works there. if you search for "mx keys" on digitec, you will find several versions of this keyboard. i think there are versions of the same keyboard that work better with windows than the one that says "for mac". try to exchange it.
Changing the battery without disassembling the keyboard will probably not work. In any case, it is not supported by the manufacturer. I've been using my Logitech Craft for a little over 3 years and have never had a problem with the battery. I assume by "German keyboard" you are referring to the ISO DE labelling? If so, you can order them via the following link: Logitech MX Keys (DE, Wired, Wireless)
I didn't find anything with the Logitech MX Keys for Mac. There may be time-limited promotions, but these would have to be initiated by Logitech. Greetings, Edwin