Cannot merge a branch with master

I have a public git repository in and I am the only member of this project. My role is Maintainer. Recently, I created a local branch then pushed it to the upstream. Then, I wanted to merge it with master so I created a Merge Request and I put myself as the assignee. The pipeline passed successfully but when I go to the Merge Request’s page, it doesn’t show me any option about merging with master and in addition, in the right pane, in the assignee and participants sections there are progress symbols turning infinitely. See a snapshot below:

It is a public repository so I am giving you the merge requests link also:

I couldn’t figure out which setting I need to modify to allow myself merge branches with master.