Currently, Gitlab has an integration through an add-on and it only works on Jira Core projects, so it's not possible to integrate with next-gen.
We have a feature request suggesting Jira support Gitlab the same as its support Bitbucket/Github:
Please, click on vote and watch to receive updates about the feature.
Thank you for reaching out to Atlassian Community!
I searched for updates regarding this integration and couldn’t find any information for team-managed projects.
I installed the add-on GitLab for Jira and it shows the “Add feature flag” option on team-managed tickets.
Have you tried following the steps of their documentation to integrate GitLab with Jira?
On the feature requests tickets, there is no further information about the integration:
Hi All! We’re excited to share the launch of an announcement banner that lets Jira site administrators communicate directly to their users across their Jira Cloud instance. ...
Connect with like-minded Atlassian users at free events near you!Find an event
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no Community Events near you at the moment.Host an event
You're one step closer to meeting fellow Atlassian users at your local event. Learn more about Community Events