What does Yarn aim to achieve?

I created a new project using the recently released Yarn v4, installed express and typescript, and then installed @types/express. But typescript says there is no type declare file even though @types/express should have been installed.
I wondered what was going on and looked in the directory and found that there was no node_modules folder.

That in itself is fine, it probably stores the package in one place somewhere like pnpm, but it seems strange for a package manager to install a package and not have it installed. That's why I have to learn PnP or something of its own and do some additional tasks so that the typescript project can be started.

I think pnpm is a good tool in that respect. It offers flat and clear dependency resolution, storage saving with Store and other features that would be nice to have without additional learning.

All developers are busy, they don't have time to spend their learning time on a package manager.