Can I delete files from MacBook after a backup?

NO. What you are describing is an ARCHIVE.

Time machine promises to keep copies of the files that still exist on your Mac. As time goes on, Time machine backups are consolidated and older backups are removed. Eventually files not currently present on your Mac will be discarded, by design.

CherylS23 wrote:

after I back up via time machine, I should be able to start deleting files from my Mac, correct and it will be saved on time machine?

Well that is the idea of a backup.

If you value your user data—3-2-1 Backup Strategy: three copies of your data, two different methods, and one offsite.