Restrict Time Machine Backup to a certain size

From https://www.defaults-write.com/setup-a-size-limit-for-time-machine-backup-volumes/

Setup a size limit for Time Machine backup volumes

October 22, 2012 by Mr.R

Time Machine will standard use all the available disk space on an external drive or a external server volume. You can setup a limit how much disk space Time Machine may use. Use this defaults write Terminal command:

defaults write /Library/Preferences/com.apple.TimeMachine MaxSize 405600

Where MaxSize 405600 is the MB equivalent of 400GB (400 * 1024)

To remove the limit:

defaults delete /Library/Preferences/com.apple.TimeMachine MaxSize