The extra inning rule is one that has been used in the Minor Leagues for several years. The FAQ about this season on MLB.com explained it this way:
With a tight schedule and a desire to limit time on the field, the Minor League rule for extra innings will be in effect. That means every half-inning after the ninth will begin with a runner on second base. The designated runner would be the player who made the final out in the prior half-inning (or a pinch-runner for that player), and the pitcher would not be charged with an earned run if that runner scores (it would be scored as if the runner had reached on an error).
Please note that this rule is only in place for 2020 and only in effect for the regular season. Extra innings in the postseason would not begin with a runner on second.