cameo wrote:
I purchased a BT 4.0 mouse that can also be used az a USB wireless
mouse, using a 2.4Ghz USB dongle. It works fine on my Win10 Lenovo
laptop in either mode, but on my older HP Win7 PC the BT connection does
not work. I wonder if it is because my HP laptop does not "understand"
the BT 4.0 standard or what? Could it be because the BT 4.0 mouse is not
downward compatible with possibly an older BT standard used by my Win7 PC?

Just check in Device Manager on your Win7 PC which Bluetooth version
the Bluetooth adapter supports. It should specifically say '4.0'. (Mine
says 'Realtek Bluetooth 4.0 Adapter'.)

As to whether the Bluetooth mouse is compatible with earlier/lower
Bluetooth standards than 4.0, just check its specs, either in TFM or or
the manufacturers website.