Najafi Q&A: Congregational Prayer

If the congregational prayer is being held, is it valid for someone to pray individually, especially if it is an audible prayer and the imam can hear the recitation of the individual? If it is not permissible, does the prayer become invalid or is there only sin involved?

In the month of Ramadan, is it better in congregational prayer to limit it to Maghrib and ʿIsha only—leaving out the Maghrib nafilah—and to shorten Maghrib and ʿIsha by reciting short surahs such as al-ʿAsr or al-Nasr, performing the smaller tasbīḥ in rukūʿ (Subḥān Allāh three times) and likewise in sujūd, and offering a light qunūt such as restricting it to “O Allah, bless Muḥammad and the family of Muḥammad,” or “My Lord, forgive me and have mercy on me,” and similar short supplications? Or is it better to perform the nafilah and not lighten the obligatory prayer, by reciting the larger tasbīḥ in rukūʿ and sujūd, combining both the larger and smaller tasbīḥ in them, and performing the prescribed qunūt such as Duʿāʾ al-Faraj and others?

Is outward righteousness sufficient to establish the justice of the imam of congregational prayer (Imām al-jamāʿah)?

The correctness of the prayer leader's recitation is a condition for leading the congregation in prayer. It is not permissible to follow someone who does not recite well. So, is it permissible to follow someone who does not recite well, with the understanding that the prayer is not valid and the person must repeat it later? Knowing that following the leader is done for some benefit, such as the hope of gaining reward or increasing the number of worshippers?

If a person does not consider himself just, either because he does not possess justice in reality or for some other reason, is it permissible for him to lead the congregation in prayer if the congregants believe him to be just? And if he does lead the prayer, will he have committed a sin?

Should congregational prayer be relatively quick to make it easier for the elderly and not be a burden on them?

A certain mosque guard expels worshippers from the mosque and does not allow them to enter under the pretext of COVID-19, although the number is small, the mosque is large, and only those who want to enter are allowed. Everything has returned to its normal state except for this mosque. Is this action correct?

In the congregational prayer, if the follower raises his head from bowing before the leader and remains standing intentionally without returning to bowing to follow the leader, is it ruled that their congregation is invalidated?

I pray in a mosque, but I do not believe that the leader of the prayers is a just man. However, if I leave the congregation prayer, the people who pray there will notice that. This might be bad for the leader and make the praying people separate into two parts. My question is: Is it permissible to pray behind him without the intention of a congregational prayer?