I don't see where microservices or not have much to do with having a monorepo or not. We have a monorepo and we have both. We have "microservices" and we don't. It's also a huge variable term. What I call microservices you guys might call "a bunch of monoliths communicating with each other". Same difference.

git bisect helps to easily identify hard to find but reproducible bugs. Since we try to have small PRs once you found the breaking commit it is usually easy enough to the find the bug. Murphy and exceptions obviously apply.