Problem with Logitech Unify Bluetooth adapter
 

I am running Mint Debian on a ThinkPad, the build in BT has some problem some times not working, so that I used a Logitech Unify adapter. I used Solaar to setup the adapter to use with different Logitech keyboard and worked, but when I tried to pair with a Bluetooth speaker it doesn't recognize it, I don't know if that adapter only works with Logitech devices or not, any comment ?

The Logitech Unify adaptor isn't Bluetooth. Don't expect it to work with anything else. Don't expect it to work with other Logitech devices. I have 2 Unify adaptors now (2 keyboards and 1 mouse) because they aren't universal.

I never got Solaar to work for me. I'd sneak my devices onto public computers to pair them in Windoze. That probably wouldn't work today.

OIC, I remember long time ago I got a non Logitech 'dual mode' mouse, that the mouse can work with notebook via BT, or via the adapter on any PC. I did pair 2 Logitech K400 via Solaar, have not tried other models.

As posted the unifying receiver is just for unifying compatible logitech mice and keyboards. Not all logitech wireless devices are unifying.

That's different.

I have 3 Logitech devices that came with 2 'Unifying' transceivers. (A keyboard & mouse combo, and a keyboard another time). The 'Unifying' adaptor for the keyboard&mouse combo doesn't work for the second keyboard and vice-versa.

That is because the included receiver is only configured for those devices. You need to use the linux unifying software called Solaar or the Windows/Mac software downloaded from the logitech website to add devices. According to logitech website you should be able to connect up to 6 compatible devices.

https://pwr-solaar.github.io/Solaar/

They weren't configured for any devices. I had to pair all my devices to get them to work in the first place. As I couldn't get Solaar to work I found Windoze computers and paired them. I could not pair the one with the other. Perhaps I bungled.