It seems there is a bug on the DNS page (DNS made easy addon), when adding a cname, it seems to error out with error, when discussing with support it seems to be requiring lower case, 75% sure it's a bug parsing the cname correctly. "Target for CNAME record is invalid", is the error - The context was adding a DKIM record from office365 and some of the letters in the DKIM record were capitalized.
https://learn.microsoft.com/en-us/defender-office-365/email-authentication-dkim-configure