I have watched home games in the current stadium of the Cubs, Orioles, Rays, Guardians, Rangers, Angels, A's, and Braves. Wrigley and Oriole Park are the only ones I have been to multiple times and the only ones in this list I want to re-visit.
I went to a Twins game at the old dome.
With no games going on, I have been in or around the stadiums of the Yankees, Red Sox, Blue Jays, Twins, Royals, White Sox, Mariners, Phillies, Mets, Nationals, Marlins, Cardinals, Reds, Diamondbacks, Giants, and Rockies. Fenway is the only one in this list I am sad about not watching a game.
That leaves the Tigers, Astros, Brewers, Pirates, Dodgers, and Padres. I've spent a lot of time at the DTW airport but never in Detroit. Never been to Houston, Milwaukee, Pittsburgh, or San Diego. I've seen a lot of LA, but I've never been near Chavez Ravine.