Hi there paulboh50!
Thank you for posting in Apple Communities. It sounds like you are having trouble optimizing storage space on your Mac. We have a few tips that you can use that may help.
To start, are you referring to the Optimize Storage option discussed here: Optimize storage space on your Mac
If so, go to the Apple TV app on your Mac, then choose TV > Preferences, then click Files. Is Automatically delete watched movies and TV shows enabled or checked? If not, then this may explain why Optimize Storage is disabled.
You can also optimize your mail preferences to help increase your storage space. For information on this, look here: Change Account Information preferences in Mail on Mac
We hope this helps.
Cheers!