Problems with AirPort Extreme and new Big Sur

You can connect a USB drive to the Time Capsule's USB port and use the Archive function in AirPort Utility to back up the contents of the Time Capsule hard drive to the USB drive.

But, I cannot say whether your Big Sur Mac will be able to read the data on the USB drive......because it is formatted differently than the Mac. So, I would check to make sure that your Mac can read the data on the USB drive before you erase the Time Capsule hard drive.

If you decide to erase the Time Capsule hard drive, the process will not "convert the format". The format of the Time Capsule will remain the same......HFS+.....and the hard drive will be blank.

Frankly, my advice would be to avoid trying to use the Time Capsule to back up your Big Sur Mac......because this process is creating so many problems for countless numbers of users. In other words, there are no guarantees that erasing the Time Capsule hard drive will allow things to work correctly.

It's your call on that.

Welcome to the club. Countless numbers of users are having issues with Big Sur and Time Machine backups.

So that we don't waste your time asking you to do things that you may have already done, could you please briefly list the troubleshooting steps that you have already tried?

Permissions issues......they are rampant with Big Sur......but I don't have a solution for this problem.

When you installed Big Sur, it changed the format of your Mac's hard drive from HFS+ to APFS. The Time Capsule (you are calling it an AirPort Extreme) hard drive is formatted in HFS+......and cannot be changed to APFS.

So, Time Machine has to try to back up APFS data on your Mac and change it to HFS+ data on the Time Capsule. It works for some users, but not others......like me.

If it were me, and I wanted to try to back up to the Time Capsule, I would erase the Time Capsule hard drive and try to back up the Big Sur Mac again. But, I don't use a Time Capsule to back up my Mac any longer. I back up to a USB drive that is formatted in APFS connected directly to the Mac. Works fine so far.

Sorry, I'm not familiar with this application. I have used Disk Warrior for data recovery in the past, but not with Big Sur.