From your question I gather that you don't have any specific requirements with regards to performance or technology: both PostgreSQL and JWT are well-supported in both ecosystems and so my recommendation would be to go with whatever you're most familiar with already which seems to be ASP.NET if I interpret the wording correctly.

Although there are very good frameworks and libraries for Go, you'll be looking forward to doing a lot of things manually. Although this can potentially lead to very optimized and high quality software, it can just as well slow you down because you're dealing with low-level stuff that doesn't actually add business value to your application.

The point in favour of Go would be that you can easily deploy it to Heroku, which (afaik) doesn't support ASP.NET.

As you're a one-man team, you might even want to reconsider the decision to have separate codebases and languages for back-end and front-end. You're going to need to be very focused on adding business value to your application without getting distracted by some low-level technical detail or context switch. With React being your chosen front-end technology, I'll throw Next.js in the ring. (It'll deploy on Heroku nicely, too).

In the end: choose the technology that will support your flow the most.

keedrop