An exclamation point warning use to show up when loading a world from a previous version to a latest version. As of 1.14.3, the exclamation point warning no longer shows up.
How to reproduce in 1.14.2
While in 1.14.2 make a new world
Quit Game
Load 1.14.3
Point mouse cursor at a world made in 1.14.2
How to reproduce in 1.14.3
While in 1.14.3 make a new world
Quit Game
Load 1.14.2
Point mouse cursor at a world made in 1.14.3
The exclamation point will only show up in snapshots and pre-releases, see MC-136306