I got this kind of solved by reducing all levels on the equalizer. Ok.
Now I have another issue, the volume with my BT car radio is far too low, it's about half of the volume of other sources. I already have reset the Equalizer and set the media volume to max on the phone.
Beside that it would be desirable to have separate equalizer and volume settings per BT device.
My old Redmi Note 5 with Android 9 custom rom did not have these issues and restored the last volume per BT device.