Columnstore tables and indexes are always stored with columnstore compression. You can further reduce the size of columnstore data by configuring an additional compression called archival compression.
For columnstore tables and indexes, all columnstore tables and indexes always use columnstore compression and this is not user configurable. Use columnstore archival compression to further reduce the data size for situations when you can afford extra time and CPU resources to store and retrieve the data. You can configure columnstore archival compression.
Reference:
https://docs.microsoft.com/en-us/sql/relational-databases/data-compression/data-compression
https://docs.microsoft.com/en-us/sql/relational-databases/data-compression/data- compression?view=sql-server-ver15