Why is this synchronization so difficult?
So my storage is full again. Then I took lots of files and put in a library I DON'T SYNC, removing the files from the synced folders. I removed LOTS OF FILES, but my storage is still full. I replaced my online lib with my local one and nothing changed regarding my storage. I'm sick of these problems. WHY IS IT THIS WAY?
In general, micro-managing your storage is going to be hard, that's just not how Zotero is designed. You can disable file sync, you can use a webDAV, or you can pay for more storage, but trying to move stuff around to free up storage, in ways that I don't think you fully understand (a non-synced library isn't what you seem to think it is) is just going to cause the types of problems you're seeing, which are then made worse by additional off-label troubleshooting.