We have a local independent league team where I live. MLB uses them to experiment on for rule changes. A couple of years ago my son and I went to a game where they were using a robo ump to call balls and strikes. They did have a home plate ump but he wasn't calling balls and strikes so you had to look at the score board to tell what happened. They might as well have given him a chaise lounge and a cooler of beer during the game.
Baseball's 'robo umps' explained: How automated strike zone works with challenge system expanding in minors Major League Baseball could see 'robo umps' and a challenge system by 2026 Dayn Perry