Time Machine completed a verification of your backups. To improve reliability, Time Machine must create a new backup for you.

The problem occurred because your Time Machine backup file has become corrupted and is no longer useable. Unfortunately, there is no "fix" for this issue, which has plagued countless numbers of Mac users.

Click on Start New Backups to erase your old backup files and create a new backup file.

Once this issue occurs, it tends to repeat itself every few months or so, so if your backups are important to you, you might want to consider a different method for your backups. The most reliable backup solution would be to connect a USB hard drive directly to your Mac to back up in that manner.

this has been happening every few months.

Your Time Capsule is now likely 5+ years old. That explains a lot, as well as Big Sur, which does not get along all that well with Time Machine backups to a Time Capsule.

I also have a hard drive for each computer on my network used for Time Machine backups. Redundancy is my friend.

Smart move.