Express is extremely mature as a backend, although you may not like the middleware patterns compared to Flask, for example. I've used Flask for years, and find these similar, with some differences.

Next.js + Vercel has strong adoption. This probably comes the closest to checking all of your requirements, although I wouldn't suggest using this for all use cases.

IMO the Node backend framework ecosystem is more mature than Python (no idea about .NET) since Python really is positioned better for data science/ML, etc.

Express itself might be mature but it's a fraction of what you need to make a full application.

The JS backend ecosystem is definitely not mature. Eg: ORMs are still being figured out. People are migrating en masse to Drizzle which hasn't even reached 1.0. The best (fastest, better features, etc) PG driver for JS is Postgres.js which is maintained primarily by a single guy. Etc.

Next is a bad option IMO. They keep experimenting while having users on board and introducing breaking changes. The performance for SSR is terrible. Hosting it outside of Vercel is a road full pain. Etc.

I've never used Python but Django (or Rails, or .NET, etc) are more mature than most of the NPM ecosystem.

It sounds like you're looking for a Django/Rails type framework for JS-- you're not really going to find this. Javascript isn't really the ecosystem that's going to give you something opinionated, although it'd be a nice addition.

I'm not sure you're giving JS it's due. Prisma is an excellent ORM-- it makes Sqlalchemy feel clunky. I'm not sure about your comment on SSR performance either, although I do agree that Vercel tends to be a lot of pixie dust on top of EC2.

What have you used previously?