CKEditor 5 Collaboration Server, when deployed on-premises, supports MySQL and PostgreSQL for its SQL database. The CKEditor Collaboration Server, in addition to SQL database, also requires Redis, which is supported with single instances as well as cluster setups.
CKBox On-Premises also utilizes MySQL and PostgreSQL. The maximum supported file size for storage via SQL is 4GB.
For detailed configuration and setup instructions, refer to the official documentation: