Max 3 PDBs within 21c Standard Edition S2, not bad

While the feature “Multi-Tenant” begin within 12c, now is a mandatory for both Editions “Enterprise Edition” and “Standard Edition S2” beginning with 20c.

Note: If you want to create mode than 3 PDBs within 21c, we have got this error:

Recommendation: while you want to upgrade to 19c, it is better to upgrade as a PDB 19c and be familiar with the features Multi-Tenant, because no more NON-CDB starting whit 20c.