OpenGL has been with Minecraft Java from the very beginning, but it has not received updates for a long time and creates real problems. The key incentive to action was Apple: macOS will soon stop supporting OpenGL on new devices, which would threaten the game's operation on Mac.
Vulkan is natively supported by Windows and Linux, and on macOS it works through a proven compatibility layer, which will ensure the stability of Java Edition on all three platforms. The transition will provide access to Vibrant Visuals, graphics improvements that were previously only available in Bedrock. For ordinary players, the changes will be almost imperceptible, unless they use mods.
The main difficulty awaits modders: they will have to adapt their modifications to the new architecture. Mojang has promised full support for mod creators throughout the migration. The changes only affect Java Edition; Bedrock remains unchanged.