I know a little more now.
The querty keyboard I was talking about is a Model KS45B-2 from the manufacturer SEENDA
https://www.amazon.de/seenda-Multi-Devi ... B08RP44ZRZ
I checked with my Android Phone and I checked with the Adafruit LE connect v3.3.2 App that it is a Bluetooth LE keyboard
Interestingly it shows up three times with different Addresses there:
1. C7:BB:0E:4F:71:FD
2. C7:BB:0E:4F:71:FE
3. C7:BB:0E:4F:72:00
The ItsyBitsy nRF shows up with F6:11:64:44:8C:0C address.
I will attach screenshots from my Android phone about this
The Seenda Keyboard uses a Nordic Semiconductor Chip with UUID 2A29 / Firmware: 2A26 and a PNP ID: 2A50
It offers DFU Service, Generic Access 1800, Generic Attribute 1801, Battery Service 180F, HID Device 1812 with different Portocols and Reports
a Boot Keyboard Input Report, a Boot Keyboard Output Report and HID Information.
Also here Screenshots from Adafruit LE connect attached to this mail.
It seems when you press one of the three "Bluetooth-Keys" on this Keyboard the current Keyboard HID device "goes away" and the selected Keyboard HID device comes up.
I can see this in Settings Bluetooth on my Windows PC.
Interestingly I can not get into the Info page of the ItsyBitsy Bluetooth Keyboard (Name: MyKey by BBTF) in the Adafruit LE connect app because it "stuck" with Checking updates...
Screenshot attached.