You could use separate tools for those tasks. JIRA/Bugzilla/etc. for issue tracking, Sublime Merge or equivalent for comparing a dev branch to a main branch, and CI/CD with Azure Pipelines or whatever the “modern” equivalent of Jenkins is.

That isn’t as convenient as an all-in-one tool, and might not be what the user you’re responding to is doing. But it’s doable.

Mailman provides decentralized issue tracking.