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
Environment
Version - 1.14.3
iMac (21.5-inch, Late 2015) - CPU: 2.8 GHz Intel Core i5, RAM: 8GB 1867 MHz DDR3, Disk: Macintosh HD, GPU: Intel Iris Pro Graphics 6200 1536 MB.
Duplicates MC-154271.