Copilot unusable since the latest UI updates were forced on users

The symptoms point to more than one failure, so one broad reset is unlikely to help. I would preserve evidence from an affected chat before clearing browser data: copy its URL, conversation title, approximate message count, last date that loaded correctly, and the UTC time of each failure. If a thread opens even once, move the important facts into a Word or OneNote document immediately rather than relying on that thread as the only copy.

For the OneDrive-folder issue, test a new folder containing two small files with ordinary inherited permissions. Add that folder as a resource and ask Copilot to name both files. If individual files work but the clean folder does not, report it as folder enumeration rather than file access. Include whether the folder is personal OneDrive or SharePoint, whether shortcuts are involved, and whether the same account can open every file on the web.

Long conversations should be reported separately with the conversation URL and request/correlation ID from the failed load. Start a continuation chat with a manually reviewed summary while the original remains intact. Do not delete the original, repeatedly reinstall apps, or remove its project until Microsoft confirms whether history is missing or only failing to render.