Oracle introduced a new mechanism to extend the maximum string size for VARCHAR2, NVARCHAR2, and CHAR/NCHAR fields up to a maximum of 32k characters rather than the traditional 4000 for VARCHAR2 and 2000 for NVARCHAR2/CHAR columns.

Setting the MAX_STRING_SIZE is not a simple setting that can be changed, it requires applying a change at both the CDB and PDB level by altering the database control file, restarting the database in an upgrade/migration mode, running a script that is provided on the filesystem within the container, and then bringing the database back online after the migration/upgrade is complete. As such, the setup for this is quite complex and I'm not sure whether we can automate such things or if a custom image will be necessary.