Well, first there is a difference between “notarization” and “sandboxing”. Notarization just requires you to have your app signed, is a completely automated process, and in no way restricts what your app does.

Sandboxing restricts what your app can do and you have to use entitlements to use certain features.

But no, notarization is not “required” and as an end user you can ctrl-click the first time you run an app to bypass it.

Still, give it more 5 years or so.

They said the same thing back when it was announced in 2010....

They also said that Apple would never make notarization a requirement, then came Catalina.

They never said that and in fact it is still not a requirement. You can use the same control click to bypass it that you always could.