panic busy timeout[0], (60s): multiple entries holding the registry busy, IOKit termination queue depth 0: 'AppleAPFSMediaBSDClient' (1,1810001), 'AppleAPFSVolumeBSDClient' (1,1810001) @IOService.cpp:5770

Fustbariclation wrote:

The exact error on my Macbook M1 (2020) is:

panic(cpu 2 caller 0xfffffe001b400bac): busy timeout[0], (60s): multiple entries holding the registry busy, IOKit termination queue depth 0: 'AppleAPFSMediaBSDClient' (1,1810001), 'AppleAPFSVolumeBSDClient' (1,1810001) @IOService.cpp:5770

This is referring to some sort of file system issue on some drive (no idea which drive, internal boot or external). Could also indicate a hardware issue with the drive.

I was just adjusting the volume at the time, with the browser in the foreground, nothing very heavy running.

Do you mean sound/audio volume? Or you were adjusting partitions on a drive? The former is irrellivent while the latter could be related.

I do not have any external peripherals connected (no USB), and I am backing up over ethernet using a disc on another computer.

Try running Disk Utility First Aid on the hidden Container located on your internal SSD. Within Disk Utility you may need to click "View" and select "Show All Devices" before the hidden Container appears on the left pane of Disk Utility. Even if First Aid says everything is "Ok", click "Show Details" and scroll back through the report to see if any unfixed errors are listed. If so, then run First Aid again until the errors are gone. If the errors cannot be fixed, then try running First Aid from Recovery Mode, otherwise you will need to erase the disk followed by installing macOS & restoring from backup.

The Kernel Panic could also be caused by some third party software you have installed. Run the third party app EtreChecks and post the complete report here so we can examine it for clues.