20 commit rule should not apply if the merge request is set to squash
If the merge request has been set to squash, there should not be any issue with having multiple commits.
It is often useful to have many smaller commits than one large commit. During code review, the reviewers may request for various changes over multiple rounds. Having small commits that are isolated to each comment make it easier for the reviewers to identify the changes that address their concerns. It allows the reviewers to also view the changes commit by commit.
If the merge request were to be rebased, the reviewers would have difficulty looking for the changes that are relevant to their comments.