I had this problem with Manjaro on my macbookpro 2016.
Now I am having same problem with Fedora 35 on PC. I googled it and some forums says it causes due to 2.4 GHz issues with Wifi.But now I am using ether-net cable and it is still happening.
It doesn’t matter what I’m playing it offline or online source. Audio becomes lag when I am downloading files.
inxi -Fzx in terminal and post the output as </> Preformatted text here.
Have also a look to pw-top to see what goes on when you open something with audio/video.
Just check, if you use USB3 to power your Bluetooth. If you need an extension cable for USB look for a good one and keep it short. Preferably use USB3 on backside …
Did you try without the mouse once, to see if the problem still exists.
I also changed Bluetooth Adapter to USB 3.2 port on the back of the PC and not using mouse at the same time.
When I am screen-recording during speedtest , audio stuttering happened.
But the screen-record video doesn’t happen audio stuttering.
Found other possible way. Open Gnome System Monitor, if you’re using Gnome or other equivalent, there find wireplumber right click, select Change Priority, change it from normal to Very High. Usually anything related sound process will on very high priority and I don’t know why wireplumber set to normal, only pipewire set to very high by default.