In order to [safely] hold congregational prayers in mosques and other places of worship, government officials in our country require congregants to keep a distance of two meters (approximately 6 feet) between adjacent individuals in any given row, and that a vacant row should be included between one row and another. Therefore, can congregational prayer take place under such conditions (i.e., is it valid) according to the rulings of His Eminence al-Sayyid al-Sistani?
A [maximum] distance of 120 cm (approximately 4 feet) is permissible between a prayer congregant and the person standing next to them in the same row and between the place of prostration of a given row and where congregants stand in the row ahead of them. A distance of two meters [between congregants], as described in the question, is problematic for the establishment of a valid congregational prayer.
Source: https://www.sistani.org/arabic/qa/02756/