No, you divide work so that the majority of it can be done in isolation and in parallel. Testing components together, if necessary, is done on integration branches as needed (which you don't rebase, of course). Branches and MRs should be small and short-lived with merges into master happening frequently. Collaboration largely occurs through developers frequently branching off a shared main branch that gets continuously updated.

Trunk-based development is the industry-standard practice at this point, and for good reason. It's friendlier for CI/CD and devops, allows changes to be tested in isolation before merging, and so on.