I was working on to setup renovatebot though self-hosted and I saw they have config:recommended where it had "group:monorepos". Why do we want to group monorepos separately when compared with other dependencies?
group:monorepos is a preset that enables grouping in dependencies part of well known monorepos.
If you use two dependencies A and B, both have an upgrade available and they are actually originating from the same Git monorepo, you likely want to update both together in the same PR/commit. That's the purpose of this preset.
Otherwise, you'd get two PRs: one for A and for B.
Why do you want that? Because there are chances that you need to upgrade both A and B at the same time for them to work properly. Or at the very least for consistency, even if they'd work separately: why would you upgrade only one?