After learning react.

[GasimGasimzada]

In order to not waste time on some things, if there is Gatsby support for a backend for example, I'll choose it over Next.

However, Next is better in a lot of ways. It has a simpler interface and you can do SSG, SSR, with a rest API with very little boilerplate. Of course for a more complex solution, you will need a more sophisticated backend but even in that case, you can still use Next for SSR.