MeStrak

NestJS is an excellent framework (they both are). I would say the fact that you're working with Angular makes NestJS a great match, unless you're splitting front and back end between developers. But even in that case I would still go with NestJS for a new project.

Regarding the single threading point, take a look at PM2 which helps to run Node in multiple processes (we use it with NestJS) https://pm2.keymetrics.io/docs/usage/cluster-mode/

Also regarding web server performance in general this is an interesting post showing how Node with outperform Java in a web situation (be careful though, best to check a few posts to make sure these aren't totally biased benchmarks!): https://www.tandemseven.com/blog/performance-java-vs-node/

I also recommend NestJS based on your description. Same language as the front end which is good as there are only two of you, and the structure of NestJS apps is inspired by Angular so it will feel very familiar. JWT and MongoDB also well supported (obviously that's the same for Spring too though).

We use it for all web applications, it's a great framework.