Recently, Time Machine Backup stops while ”cleaning up”, every time.

Recently, Time Machine  Backup stops while ”cleaning up”, every time.  This has happened on four different portable hard drives.  I have used Time Machine for years without problems.  It happens on all Hard Drives, including a newly reformatted Drive.  Using MAC OS 15.0, on Macbook Pro.  Perhaps the Time Machine App is corrupted, but I can find no way to “restart” it (turn off, then on).