At two packages sharing types, yes — but keep it boring. npm/pnpm workspaces are enough:

1{ "workspaces": ["apps/*", "packages/*"] }

1{ "workspaces": ["apps/*", "packages/*"] }

The payoff is that a type change and the code reacting to it land in one commit, and there is no publish step between them. That is worth a lot even at this size.

What you should skip is the heavy tooling — Nx, Bazel, remote caching. Those solve problems you get at fifty packages and a twenty-minute CI run, and they cost real setup time now.

Counterpoint: if the shared surface is genuinely just types, a single types.ts copied between two repos costs less than a workspace setup, and you can always merge later. Monorepos are easy to adopt and hard to reverse.