MGMTDB is mandatory in 12c and is claimed to be unsupported to be deleted by Oracle. In 19c Oracle made it optional.
MGMTDB frequently creates problems, such are high CPU usage and in our previous case it became bigger than ~40GB, so disk where OCR files were located had less free space because of MGMTDB.
Do you know why is it unsupported to be deleted in 12c? And have you even used MGMGTB in anything?