New Outlook Unable to Close Since build 26220.8754 Update

Hi, since this started right after an Insider build and Reset only helped once, it sounds more like a build/app regression than a normal profile issue.

I would try:

1. Check Microsoft Store for an Outlook app update.

2. Repair or reset Outlook again, then reboot before opening it.

3. Test whether closing works from the taskbar right-click menu or only fails from the X button.

4. Use Feedback Hub and include the Insider build number, Outlook version, and a screen recording if possible.

5. If you need stability, temporarily use Outlook on the web or roll back from the affected Insider build if that option is available.

The main thing is to report it through Feedback Hub because Insider build UI regressions need telemetry and repro details to get fixed.