Optimising mac storage with Photos - unable to offload from the hard drive

Is the 256 GB SSD an external drive, or do you mean that to be the internal drive for you MacBook? I'm going to guess that you mean the internal drive. Do you always have the MacBook plugged in at a desk, or do you use it as a portable? I'll guess portable.

Switching back and forth between "Optimize" and "Download" mostly produces a confused result. With "Optimize" turned on, some of your picture files will be smaller, while others may be full sized. Photos tries to use smaller images only when necessary, and will keep larger versions of the files that you're using. Switching to "Optimize" doesn't guarantee a smaller Library.

If you want to not use Photos on your Mac, you can turn off Photos Settings>iCloud and then delete the Library. That's not a bad idea. But you could afterward create a new empty Library (close Photos and then option-click on the Photos icon,) turn on iCloud and "Optimize," and then let the new Library fill from iCloud. You should end up with a much smaller Library on your Mac. If you don't like that, you can delete it again.

If you use your MacBook as a desktop, then you could use an external drive to hold your Photos Library. I say this for a desktop, because the Library really should be left plugged into the computer. See this:

Move your Photos library to save space on your Mac - Apple Support

You should keep at least 10% of your internal drive free. The Mac uses that for temporary storage, so when it's near full it really slows things down, and you may begin to get crashes.

Let us know if this makes sense, and what you do-- or if you need clarification....

I understand "queasy" -- I'm glad it worked!