The „modern“ way of development is overcomplicated and not suitable if you are an solo founder, too much time is lost on infrastructure, setup etc. The modern complicated js stack where you need to maybe configure everything for 1-2 days and need to constantly fight webpack is not how you should built an web application as a solo founder.
You should be able to be „live“ in a few minutes. For every language there is a stack enabling this, they are not the most fany ones but get their work done. Take for example laravel with spark (https://spark.laravel.com/), for 99$ you get a login-system with teams and subscription management all-in-one within minutes. And don‘t build a ci pipeline, complex kubernetes cluster or learning a dozen of aws servers. A simple VPS or root server and Laravel Forge (https://forge.laravel.com/) or Ploi (https://ploi.io/) and you are live.
As a solo founder you need to find a way to cut down on non-programming and non-marketing tasks. This means maybe not working with the hottest tech stack of the day but simply using a workhorse solution which lets you get shit done quickly.