I had the exact same issues until I found a tool that completely changed how we manage our repositories. The tool is called Git X-Modules and you can check it out at https://gitmodules.com/ right there. It is a server side solution that lets you sync directories in your repository with external repositories, so you can effectively build a monorepo by composing multiple Git repos together. What I really like is that it works without adding any overhead for developers, they just use regular Git commands. When you push changes to the parent repo, the X-Modules automatically update the external repositories. If there are conflicting updates, the tool turns one into a pull request instead of breaking everything. It also supports branching and tagging across repositories, so you can manage cross-repo changes seamlessly. We used it to migrate to a monorepo without disrupting our workflow and it has been a huge improvement over submodules.

That sounds exactly like what I have been looking for. A server side tool that handles cross-repo syncing without extra developer overhead would save us so much time. I will definitely check out Git X-Modules and see if it fits our workflow. Thanks for the recommendation.