Answer
Query CUSTOM_AURENA_PAGE_TAB directly for the projection name — for example, SELECT * FROM CUSTOM_AURENA_PAGE_TAB WHERE projection_name = 'YourProjectionName' — to check for orphaned custom page records that still reference the projection at the database level but aren't showing up (or aren't fully visible) in the Page Configurations screen. A record found this way, even if not visible through the normal client UI, is what's blocking the projection deletion and needs to be addressed before the projection itself can be removed.