I'm not 'enrolled in the Apple Developer Program" (i.e., I'm not paying Apple a sub.) Does this mean I can't notarize my apps? I tried to follow the instructions, but when I Upload my app to Validate it, I get an error, saying that my Team is not enrolled.
My Team is created from my Apple ID, and Signing Certificate is set to "Development".
Is that sufficient to create an app that GateKeeper will let through the gate?
Signing/Notarization for non-paying devs
Since no one else knows how to create an app that passes quarantine: the answer seems to be "No".
Every app is suspicious, unless you pay Apple.
As long as you sign your app, you and others can run it.
However, if it is not notarized, on recent OSs, users will see nasty warnings when they download it or attempt to open. On Catalina, they'll not usually be given the opportunity to even open the app.
Notarization is an extra step which ensures the end user that your developer ID has not been compromised. Users can right-click (or control-click, or tap-with-two-fingers) your application and choose Open from the contextual menu. They'll see a similar dire warning about Apple being unable to check if the app is dangerous, but they can click Open in that dialog.
In short, Gatekeeper will let it through, but only with explicit user consent (and most users won't know to right-click and choose Open).