Is one who misses congregational prayer – even though it is held in the mosque – sinful, based on the opinion of those who say it is a communal obligation (fard kifaya), or other opinions that do not necessitate attending it?

There is no sin upon one who misses prayer in the mosque, according to those who hold it to be fard kifayah (a collective obligation), as long as there are others performing the prayer therein. However, a Muslim should not limit their concern to avoiding sin; rather, they should strive to multiply good deeds. Congregational prayer in the mosque multiplies the reward due to the large number of worshippers, the reward for taking steps to the mosque, waiting for the prayer, the angels' seeking forgiveness, and the first row. The Prophet (peace be upon him) encouraged the virtue of early arrival and prayer in the mosque, saying: "If the people knew what is in the call [to prayer] and the first row, and they could find no way to get it except by drawing lots, they would draw lots for it. And if they knew what is in coming early [for prayer], they would race to it. And if they knew what is in the 'Isha' and Fajr prayers, they would come to them even if they had to crawl." As Al-Bukhari mentioned concerning those who miss the mosque: "By Him in Whose Hand is my soul, if one of them knew that he would find a fat piece of meat or two good ribs, he would attend the 'Isha' prayer." So strive to perform prayer in the mosque; perhaps one step will be your salvation on the Day of Resurrection, when a person will flee from their loved ones seeking a single good deed.