Wifi slows down when Bluetooth headset is connected in Ubuntu 20.04
I faced the same issue some months back and get it solved by using Wi-Fi on 5 GHz band. Basically, bluetooth uses 2.4 GHz band. If Wi-Fi also uses the same band, there will be some interference between those. So, changing the Wi-Fi to 5GHz band and using bluetooth on 2.4 GHz solves the problem.
In my case, when Wi-Fi is connected, bluetooth headset's latency was increased. And after doing some research online, I found the solution. Switching bands greatly improved things.
Hope this helps! :)