Formula One unveiled a 23-race calendar for 2021 on Tuesday, its biggest ever, but the slot that was to be occupied by Vietnam has been left vacant. The season will start in Australia on March 21 and includes the first-ever race in Saudi Arabia on Nov. 28. The Vietnamese organisers said their race originally scheduled for April might never take place. F1 organisers said they expect spectators to return next year. “The plans for 2021 have involved extensive dialogue with all promoters,” F1 said in a statement.