I set up several projects in a monorepo recently using Yarn 3, and while the end result was awesome, the path to success was dark and weedy.
It seemed I was constantly 95% of the way there, but some detail or another wasn't quite right. Yarn has no solution for this, because the problem is the integration of tooling. eslint, typescript, prettier, jest, relay, you name it. They each want to work together and integrate with each other in different ways, using various sources of truth, and so on. Then your IDE needs to adhere to the same protocols, but various extensions have different opinions about default configurations.
Along the way you really need to know your tooling deeply, or you're in for some suffering.
Relatively simple projects with full buy-in of Yarn 3's tooling are probably pretty easy. Once you get relatively complex though, I don't know, I don't think any of this is easy.
It does sound like Nx handles a bunch of this stuff for you, which I'd love to try out. I really like that Yarn isn't particularly opinionated though. Once I had things set up, there was very little to change or that could break. The scaffolding was fairly plain to see, easy to work with, and we owned it. With something like Nx where things reportedly "just work", I worry it would be an unsettling blend of black boxes and black magic making my tooling and code work... Until it didn't, at which point I'd wish I used something less opinionated.
