Again, I go back to the sub-module approach with some small amount of automation built around that. Managing sub-modules kinda sucks, but if you use it as a reference to all of the products in production and as a synchronization point for delivery, then it gives you all the benefits of the monorepo, without the performance issues.
> For this reason I'm personally always hesitant to recommend monorepos as the be-all-end-all.
May be not a monorepo, but at least trying avoid having too many repos.