OSD wizard (AWS), inside "v Advanced Encryption" section, marks "Encryption Keys" with a red asterisk meaning it's required:

ROSA wizard doesn't have asterisk on same field.
I see no reason for difference, should harmonize one way or other.

IMHO it should not have an asterisk. It's a radio buttons field, they have a sensible default ("Use default KMS keys") good enough which you can proceed to next screen, and the whole thing is in a collapsed-by-default section because it's OK to leave untouched.