In the past I've used Rails, Django, and other web frameworks with angular and some react or jquery for the front end, and either postgres, mysql or sql server for the database.
If you were to build a new web app product with a fairly complex database schema and functionality, what tech stack would you use as a starter? Obviously things depend a bit on the use case, but let's assume it's a web application that doesn't need high concurrency.
More like building a PoC of a web app start-up that can scale for a few years.
Most known and good frameworks can do what you want. If the product becomes succesfull, scaling up your team with good engineers is harder than scaling the product.
As long as you can do raw queries on your complex database, I do not see how a backend framework you don’t know yet will help you. You will sell the product, not the framework it is running on. If your current stack is still widely used in the industry, focus on the product, not on new tech
Small addition: if it is for hobby or learning: pick one new framework and keep the rest of the stack.