TIME CAPSULE SAYS NOT ENOUGH SPACE TO BACK UP MACBOOK PRO

Apple never really told us that Time Machine is only capable of erasing very small "incremental" backups to make room for new small "incremental" backups, so when the Time Capsule hard drive is close to full and you try to back up a significant amount of data like an operating system update, new images, etc, Time Machine cannot delete enough data to make room for a new backup.

You have two options:

1) If you want to keep all the old data on the Time Capsule, use the Archive feature in AirPort Utility to copy all of the data on the hard drive over to another USB drive, then erase the Time Capsule and start over with a new backup and move forward.

2) If you really don't need all the old data on the Time Capsule that goes back weeks, months, even years, simply erase the Time Capsule drive and start over again with a new backup and move forward.

It is long time since Time Machine actually managed to erase early backups.. mostly this is due to continual updates causing massive continual backups of system files.. where the required files for restoration are now so complicated and spread out over the whole backup it does not attempt anything like removing old files.

The only way to really get Time Machine moving again is to erase the TC. If you wish to keep the old backup run archive beforehand to a suitably sized USB Mac formatted drive plugged into the TC.

If you have Catalina on the computer this can also be expected to have major issues since it needs to start a whole new backup. Catalina uses such a different structure of files on the hard disk it is backed up to a differently named backup to any previous version. And it has trouble doing this to such an old design as the TC.