You could use command below to enable Mail Tip for external recipients:
Set-OrganizationConfig -MailTipsExternalRecipientsTipsEnabled $true
It works for all Microsoft client.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.