Select any commit in the graph, such as the newest commit on a pull request you're reviewing, and choose Run in isolation. SillyGit checks that commit out into a private copy of the repository, installs dependencies when they've changed, and runs your project's command there: npm run dev, ./gradlew bootRun, dotnet run or whatever you've set.
Your branch and your uncommitted changes stay exactly as they were. You don't stash anything or check anything out, and you can keep your own working copy running alongside to compare the two. Files a project needs but never commits, like .env and local.properties, are copied into the private copy for you.