No, not the Seinfeldian definition of shrinkage*, but actual physical height shrinkage due to the debut -- Opens This Week at a ballpark near you!! -- of the Automatic Ball/Strike system (ABS).
So since the size of home plate never changes (even when the other three bases grew a few years back) the tricky part of balls and strikes has long been the upper and lower limits. ABS 'solves' this by placing those limits at fixed percentages of each player's height. To do this, of course, you need a uniform way of measuring everyone and that's where there's a new sheriff in town since, obviously, individual teams can't be trusted to be their own arbiters.
The new process run by MLB has strict guidelines: no shoes, no hats, knees exposed, heels together, back against the wall, no slouching. Players are even required to be measured between 10 AM and noon on their scheduled day so as to rule out any normal shrinkage during the day (you are shorter at night than in the morning).
So meet the initial poster boy for all this: infielder Gavin Lux and note the difference between his 2025 Cincinnati Reds official bio and his new one with Tampa Bay
Severals other players have dropped multiple inches as well.
* As far as I know, MLB does not measure this particular part of the anatomy although it wouldn't surprise me if this is an actual, though rarely talked about, part of the NFL combine.