When a merge request it's created from an issue, this title it's generated:
Draft: Resolve "issue"
How can I modify the default behavoiur? Ideally to me should be fine just
Draft: Issue
There is no way to change this precise default behavior for MR titles. However, there are a couple open feature requests related to this capability: #16080 and #22209.
The closest thing would be to create a default template for MRs. However, this is only for the description, not the title.