Is the Umm Al-Qura calendar incorrect for determining the time of Fajr prayer, and should the prayer be delayed by half an hour after the Adhan, taking into account that the prayer is established immediately after the Adhan on crowded days in the Haram?

Umm Al-Qura calendar has been endorsed by a group of scholars. It is far-fetched that it would be half an hour ahead of the prayer time. One should act according to the calendars approved by trustworthy scholars, unless it becomes apparent that they contradict the شرعي (Sharia-compliant) signs.