Minecraft 1.14.3 - Screen tearing Bug.

A Screen Tearing Bug - When V-Sync is on the bug primaries occur at the bottom of the screen, when V-sync off frame rate drops occur.

Read this forum for more info - https://www.minecraftforum.net/forums/support/java-edition-support/2971246-macos-minecraft-1-14-3-screen-tearing-with-vsync