You can use nginx reverse proxy with basic HTTP auth over SSL. Or even better set up a two factor auth system with nginx. You'll probably need to set this stuff up in nginx server blocks, I think NPM is pretty limited in what it exposes to the GUI.
I'm not sure what ZM capabilities were but for notifications and stuff like that you can use Home Assistant. That also has some pretty good remote access features if you can put in the time to set it up.