WiFi & Bluetooth Coex not working properly (Interference)

I plugged in a CRS USB Bluetooth dongle on mi 2019 27' iMac and after that my bluetooth became a lot unstable. The mouse was literally unusable and when using the AirPods the connection would drop randomly. I did a lot of research but I found nothing.

I did all of the following:

-Restore bluetooth module

-Delete .plist preferences

-Reset SMC

-Reset NVRAM

-Reinstalled macOS - To a previous version (Mojave) and to the newest one (Catalina)

-Run hardware diagnosis - Everything was fine

Nothing worked, bluetooth continued to fail and drop. I even talked to some apple support and neither them could help me. All was leading to a hardware issue but I refused to believe a simple usb dongle messed up the hardware itself. What is interesting, is that turning off Wi-Fi fixes the problem. That could be because interference but I discarded it because previously it wasn't happening with the same router and also that the connection is on the 5GHz band.

The problem in Bluetooth Explorer was showing up as the following error: updateChainPower error: -3903, which means (I think) that the bluetooth module is not receiving enough power to maintain a stable connection. Also Bluetooth Explorer > Tools > Wifi & Coex Status shows this:

So my conclusion is that the USB dongle triggered something on the module firmware that now prevents it from getting enough power to work as it should. What's interesting is that if I turn off WiFi Bluetooth works perfectly.

I tried to completely erase my disk (deleting also the EFI partition), changed the partition table to MBR, then back to GUID. With a completely fresh disk drive, I installed macOS Mojave through internet recovery. That seemed to fix the issue as now I can use the mouse without any lag and my AirPods just fine.

After one day of Mojave use and after I checked that everything worked as it should I decided to update to Catalina (10.15.5) and for my surprise, Bluetooth started acting laggier again. I gave up finally and I reverted back to Mojave with a fresh EFI install. While Bluetooth is still usable I still get the same updateChainPower error and WiFi & Coex Status still shows the same as before.

Does anybody have any idea of what is happening here? Can I fix it? Thanks.