photos and space?!

but they still stay on my computer and i only have 10GB free.... why is that?

"Optimize Mac Storage" will not immediately optimize the storage, as long as there is enough free storage on your mac. Photos will free storage, if other apps are needing storage. But if there is still free storage it will keep the photos on your mac, that are already there.

If you want to free storage immediately, start with a new, empty Photos library.

• Wait, until all your photos are in iCloud.
• Move your current library to an external drive as a backup.
• Then make the new, empty library your System Photo Library and enable it for iCloud. Your Mac will download the photos from iCloud as "optimized". The new library will be much smaller than your current library

There is a drawback, however. iCloud does not sync the faces and projects. You need the backup of your library for your phonebooks and all your faces tags. The library you download from iCloud will be like described here for a library on another Mac:

Use Photos and iCloud Photo Library on multiple Mac computers - Apple Support