Well the whole Debug Kit initialization happens via injecting
<script id="__debug_kit" data-id="40909db3-9120-4500-b87f-f2e0bc0f1a6c" data-url="https://localhost/" src="/debug_kit/js/toolbar.js?1654630629"></script>
at the end of the body. This JS then injects an iframe which then shows the Debug Kit Toolbar at the bottom.
If you don’t have that script tag at the end of your HTML then the DebugKitMiddleware didn’t run (or had problems injecting that iframe)