My Bluetooth amp isn't listed in Windows but IS listed on phone, Other devices are listed in Windows

I have a Denon amplifier that supports Bluetooth - and in the past I could connect to it from my Windows 10 laptop.

However:

1. My Denon amplifier is no longer listed in "Settings > Bluetooth & other devices" on my laptop - not even if I select "Add a Bluetooth or other device".
   
   
2. My other Bluetooth devices are still listed there and I can still connect to my other devices from my laptop
   
   
3. My Denon amplifier is still listed on my phone, which can still connect to it.

3. implies that the problem is with Windows, not with my amp. But 2. implies that my laptop's Bluetooth is partially working.

"Allow Bluetooth devices to find this PC" is switched on.

How can I fix this?

Many thanks for any help.

Dave