I have worked on projects organized both ways with git and my observation is that regardless of the choices, the right tooling can make the workflows a lot more

I have worked on projects organized both ways with git and my observation is that regardless of the choices, the right tooling can make the workflows a lot more fluent. For separate repos, share code as much as possible through a packaging system so one does not have to make a lot of refactoring across multiple repos. It sounds backward but an auto minor version update can ease a lot of merging pains in a CI environment. For monorepos, figure out as early as possible what/how things should be shared and separated. I worked on a project with 20+ services and websites that form a whole product and each service chooses its own languages and build systems but shared deployment interfaces for unified service discovery. CI got tricky as it can be blocked because of an unrelated change. I have not found the unified commit history super helpful as I only have context on a few of the services and most of the time I only look at histories with `git log my/path'.