Basically, WebXR hands are not updated (frozen), browserwindow pops up, allowing hand interaction.
Alternative
Programmatically exiting immersive mode via javascript, and showing a button-overlay in the browser.
The problem here is that you're really exiting immersive mode, which is quite uncomfortable.
Developing WebXR+WebGL feels a lot like having to re-invent the UI wheel compared to HTML elements.
Solution
A similar exit-immersive workflow like Quest Browser:
https://twitter.com/coderofsalvatio/status/1808066619014303789
Basically, WebXR hands are not updated (frozen), browserwindow pops up, allowing hand interaction.
Alternative
Programmatically exiting immersive mode via javascript, and showing a button-overlay in the browser. The problem here is that you're really exiting immersive mode, which is quite uncomfortable.