From an article in The Athletic https://theathletic.com/1555626/2020/01/23/the-new-3-batter-minimum-rule-wont-speed-up-games-but-will-have-negative-unintended-consequences/
"However, while there were 2,162 pitching appearances that lasted fewer than three batters in 2019, 1,471 of them concluded with the end of an inning or the end of the game. That leaves just 691 appearances that the three-batter minimum would have extended, and that’s before searching that sample for outings that ended in injury and thus also would have been exempt from the rule."
"Again, the vast majority of those 691 pitching changes were made for a reason, and that reason had far more to do with trying to win than it did with playing matchups. The real impact of the three-batter minimum will be forcing pitchers getting lit up to the tune of a .393/.518/.657 slash line to remain in high-leverage situations. That will alter the outcomes of games, and it could alter the outcome of the season."