Does Latest Mac Software support bluetooth A2DP protocol

You can see the profiles supported by the Apple Bluetooth controller, and paired BT headphone protocols in their services line via:

option +  > System Information > Bluetooth

The only means to use Bluetooth stereo headsets is if the headset and device support a2dp

never had issues connecting any headset or speakers with any Mac or windows computer and long ad the headset / speaker does not have an active connection with another device and the headset / speaker being in pairing / discovery mode

Simple answer, please look on the Tech Specs page on apple.com. It says it supports BT 5.3, you need to see if 5.3 is compliant with A2DP for your answer.

If they will not connect to your iMac then you need to check the headphones tech specs to see if they claim they are compatible with Mac OS. Not all BT devices are, for example I wear hearing aids that are BT so I can connect to my iPhone which works just fine. However, the hearing aids will not pair with my 2020 iMac. When I checked the hearing aids tech specs they make no claim of connecting with Mac OS therefore I cannot fault either Mac OS or the hearing aids.

So the answer isn't as complex as you think it is, simply check the headphones specifications and if they claim to connect to a Mac then see what versions of Mac OS they support and compare that information to what is installed on the iMac.