"Delete source branch when merge request is accepted" checkbox doesn't appear in project's MR

Hi everyone,

We're working on a self-hosted GitLab CE (16.4.1) and we've an issue with some projects when doing MR. We don't know why, but in these projects when we're creating the MR, we don't see the "Delete source branch when merge request is accepted." checkbox in the Merge options section:

Example 1: Project without checkbox

Example 2: Project with checkbox

We don't know why this is happening and in GitLab documentation we don't see any reference to that: https://docs.gitlab.com/ee/user/project/merge_requests/#delete-the-source-branch-on-merge

Can you please help us?

Regards