Does the Hadith: "Whoever prays Fajr in congregation will be in the protection of Allah" mean that the worshipper will be immune from all calamities destined for him on that day, or does the Hadith have another meaning?

The meaning of the Hadith (definition) is that whoever prays Fajr in congregation or individually is under the protection and covenant of Allah. Therefore, no one is permitted to harm them. If anyone unjustly harms them, Allah will hold them accountable for their injustice and demand His right from them. This is a severe warning to anyone who harms those who pray. The Hadith also encourages performing the Fajr prayer, and it shows that whoever is diligent in observing it gains protection from Allah. Conversely, whoever neglects it breaks the covenant between them and their Lord, and Allah will punish them for that by casting them into the Fire.