Yep the update message to the app doesn’t apply to existing plus customers. We’ve been told we will receive an email with our 3 options (cancel, stick for the reminder and then it cancels or switch)
For existing Plus customers this will not affect your tier. At the end of your term, you will not renew (even if auto renew is on) as a Plus customer and you have to signup again (unless that changes between now and then). This is only for the users on the ‘legacy’ Plus