I tried to do exactly what you say last week but I couldn't get it to work. The turborepo documentation seems to indicate its possible with the whole concept of "internal packages" but it all depends on the compilation step of Project B being configured to compile and bundle workspace dependencies, and a simple "tsc" wasn't doing it for me regardless of the different tsconfig settings I tried.
I made a private repo who's package JSON was `private: true`, `type: module` and `main: src/index.ts` and `module: src/index.ts`. I didn't progress down that route as stated, but I was able to consume that package. Maybe none of what I said here mattered in which case the only other thing that may make a difference was that I was using pnpm for the first time with workspaces.
If its actually possible I'd love to know how.