Photos are stored on Mac, not iCloud

[NStocks]

It may not be related to Catalina, but my hard drive has 25GB of storage made up of photos, using the stock Apple photos app only.

Everything is checked to be stored on iCloud with 'optimise Mac storage' enabled.

Why would so much data be stored on my Mac?!

 

[BlueChroma]

"Older Documents will be stored only on iCloud when space is needed."
Seems like they get removed when you run out of space while adding new files.