Everything works well when you do not have mono repo packages linking to one another. But once you start linking (e.g., @riva/shared package with @riva/portal), everything breaks down and fails to deploy.
The decision to switch to pnpm was primarily to be compatible with isolate-package which has since been tested to be running smoothly with yarn modern and classic as well.
Action: Discontinue usage of pnpm and swap back to yarn classic until Firebase starts supporting other package managers out of the box