I don’t see it freeze entirely when I try it, but typing does become incredibly slow (up to a second of latency). I’m pretty sure this the browser’s editing and layout code falling apart — if I paste that into a plain contenteditable element, both Chrome and Firefox become similarly slow. Do you have a specific reason to suspect the performance issue is in ProseMirror?
Honestly, I hadn’t considered that this might be an issue with any editable element. This assumption was based on profiling my project during editing, where I observed long execution times related to diff. I’ve attached a screenshot of the profiling results below.