When you catch the last Rak`ah of Maghrib, you should : -Follow the Imam in the last Rak`ah and recite Tashahhud. -After the Imam’s Salam, stand up for the missed Rak`ahs. -In the first missed Rak`ah, recite Al-Fatihah and another Surah. -Then go to Ruku` and Sujud, and then recite the first Tashahhud. -In the final Rak`ah, recite only Al-Fatihah, then the last Tashahhud.

There is nothing wrong with standing on one’s own behind the row for a reason, such as finding that the row is complete, as the obligatory parts of the prayer – in general – are waived when there is a valid excuse. If someone is afraid of catching some sickness or becoming infected with covid-19, so he prays on his own standing behind the row, his prayer is valid, because even though he omitted something obligatory, he omitted it for a valid reason.

Praying in congregation in the mosque is obligatory for men who are able to do it, according to the correct scholarly view, based on a great deal of evidence, including the words of the Prophet (blessings and peace of Allah be upon him): “By the One in Whose hand is my soul, I was thinking of issuing instructions that firewood be collected, then I would issue instructions that the call to prayer be given, then I would instruct a man to lead the people in prayer, then I would leave them and go and burn the houses of some men. By the One in Whose hand is my soul, if one of them knew that he would find a meaty bone or a sheep’s foot, he would attend `Isha’ prayer.”

If you pray in congregation at home or in the workplace, you do not attain the reward of praying in congregation in the mosque.

If the worshippers are spaced out in the row because of precautionary measures required due to the pandemic, then there is no longer any reason to prevent praying between the pillars, and it is not disliked (makruh) to stand in a row between them in this case.