What Azure Repos shows instead
Azure Repos gives you commit history per repository, per branch, and per push, plus file-level history and blame. All of it is list-based, and all of it is scoped to one repository at a time. There's no calendar view, and nothing that aggregates activity across every repository in a project.
Why that's a gap on a multi-repo project
A project with a dozen repositories means opening a dozen commit lists to answer a question a heatmap answers in one look: when was this person or this project actually active? Pull-request comment activity is even harder to see, since it lives inside individual pull requests rather than any single history view; see counting pull request comments per developer in Azure DevOps for what the widget catalog does and doesn't offer there.
What a calendar heatmap adds
A GitHub- or GitLab-style contribution graph turns that scattered history into daily totals across a full year, with commits and real discussion comments counted per day and broken down on hover. It's a navigation and trend view, not a substitute for reading the actual commits and pull requests.
Add the heatmap Azure Repos doesn't have
Commit Graph for Azure Repos builds a per-person contribution calendar across every repository in the current project, client-side, using your own Azure DevOps credentials.
See Commit Graph for Azure Repos