Create a new empty Pages document from a Blank template and manually save it to your Desktop. Quit Pages from its Application menu. Now, double-click on that new, empty Pages document and see if Pages opens it without crashing. If it does, then there is something wrong with the document that caused you to originally post here.
If Pages still crashes with the newly created empty document, you can certainly do the launch Pages with the shift key held approach, but if that too did not work with a subsequent open, I would do the following:
- Update Pages to Pages v15.3.1
- Update macOS Tahoe to 26.6.1
- Try opening that last created empty Pages document again with Pages v15.3.1.
If the problem still exists, it is possible that you may have installed anti-virus, or some so-called Mac cleaning app that has internally damaged the Pages application bundle. If this is the case, completely uninstall those categories of applications, reboot your Mac, and try the item 3 again.