Which of the following teams won the Indian Super League 2020–21 ?

The correct answer is Mumbai City FC.

Here is a detailed breakdown of the 2020–21 Indian Super League (ISL) season details:
• Tournament and Finalists: The 2020–21 season was the seventh edition of the Indian Super League. The final was contested between Mumbai City FC and ATK Mohun Bagan on March 13, 2021, at the Fatorda Stadium in Margao, Goa.
• The Match Result: Mumbai City FC defeated ATK Mohun Bagan with a score of 2–1 in the final to secure their maiden Indian Super League championship.
• Historical Double: Prior to the final, Mumbai City FC had also won the League Winners Shield by finishing at the top of the league table during the regular season. Winning both the Shield and the Championship Trophy completed a historic double for the club.