I also find this whole notarization thing confusing. My current Apple Developer account does not seem to support that so I “enrolled”. What the heck does this mean? I don’t know. And I have been waiting for the enrolment to complete for over a week now but that does not seem to be unusual. I hope notarization will be possible once I have upgraded (?) my account.
Will let you know in case I gain more insight.
In the meantime, this should be a work-around for your users: