I feel like I keep hitting the same wall. I can get the basic functionality of my web app finished in like 2 weeks (the actual selling point of my app). But then I get stuck for months fleshing out the basic boilerplate of any SaaS app, the authentication, email verification, forgot my password, subscriptions (upgrading, downgrading, cancelling, webhooks, etc.), support, transactional emails, etc.
How do you do it? Have you just done it once and keep reusing the same code? Are you using services to handle it all for you? Do you reroll it everytime you make a new product?
For me it'd be nice if there was a backend as a service that handled most of it for you but then it seems your too tightly coupled to that backend and can't introduce your own business logic. (I run on the MERN stack for the most part btw).