MLB has proposed to the MLBPA that that the start of the 2021 season be delayed by one month, with the season being extended by a week on the back end, playing a 154 game schedule, and implementing expanded playoffs, per Tim Brown on Twitter. This is due to the ongoing COVID-19 pandemic, and is on the heels of Cactus League and Arizona officials requesting that MLB delay the start of spring training.
At this point, any delays in starting either spring training or the season are about trying to maximize the window available to have fans in the stands.