This happens with all versions of nativescript-dev-webpack
I am trying to use pnpn with {N}. PNPM is a great tool when you work with a lot of npm projects using the same deps. This is the case when you build multiple {N} apps or plugins (i have around 40).
Now pnpm works very well for {N} plugin dev. But it does not work with apps using nativescript-dev-webpack. It won't find webpack

The issue is here. You look for webpack in the root node_modules of the project. But this will only work with flat npm installation. webpack being you dependency you should look for it relatively to nativescript-dev-webpack module folder.
This is explained in the pnpm FAQs

I hope you can fix this one.