What stack would you use to build a CRUD web app in 2020?

I think it depends a lot on what's already in place. Are you a Microsoft shop? ASP Core is your obvious choice. Already doing Django? Keep doing Django.

If the question is what stack you would choose for a personal project, I think the answer is "Whatever you think looks interesting."

https://prisma.io is a good choice, I know successful companies scaling while only running a single instance.