<!--IssueSummary start--> <details> <summary> Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards. </summary> - [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=505464) </details> <!--IssueSummary end--> <!-- This issue template can be used as a great starting point for feature requests. Learn more about the process: https://handbook.gitlab.com/handbook/product/how-to-engage/#customer-feature-requests. The section "Release notes" can be used as a summary of the feature and is also required if you want to have your release post blog MR auto generated using the release post item generator: https://about.gitlab.com/handbook/marketing/blog/release-posts/#release-post-item-generator. The remaining sections are the backbone for every feature in GitLab. The goal of this template is brevity for quick/smaller iterations. For a more thorough list of considerations for larger features or feature sets, you can leverage the detailed [feature proposal](https://gitlab.com/gitlab-org/gitlab/-/blob/master/.gitlab/issue_templates/Feature%20proposal%20-%20detailed.md). --> ### Release notes <!-- What is the problem and solution you're proposing? This content sets the overall vision for the feature and serves as the release notes that will populate in various places, including the [release post blog](https://about.gitlab.com/releases/categories/releases/) and [Gitlab project releases](https://gitlab.com/gitlab-org/gitlab/-/releases). " --> ### Problem to solve Essentially the same as in https://gitlab.com/gitlab-org/gitlab/-/issues/505462++ but when opening a merge request:  In the UI this is considered an activity, but the API field `last_activity_at` is not updated by it. ### Proposal Update that API output field accordingly. ### Intended users / Feature Usage Metrics / Does this feature require an audit event? Same as in [gitlab#505462](https://gitlab.com/gitlab-org/gitlab/-/issues/505462#intended-users)