You should update your Zotero; version 6 may no longer sync correctly. Also, you’re at the online storage limit, so some files won’t be uploaded even after the update. This only affects file attachments; all your items and collections should sync correctly after the update.

For more troubleshooting also see https://www.zotero.org/support/kb/changes_not_syncing and https://www.zotero.org/support/kb/files_not_syncing