I was playing Minecraft (1.14.4) as usual on my MacBook Air. I had the launcher set to "Keep Open While Playing" so that I could relaunch it if it ever crashes. The launcher had said that it would update next time I opened it.
The game and the launcher both suddenly crashed. I clicked it to reopen it. A window popped up saying it was updating. I waited. The progress bar didn't fully fill, but the launcher opened up and it was just a black screen.
I restarted my computer. Open Minecraft Launcher, black screen again. I restarted several more times, same problem.
I emptied the contents of my Minecraft game, deleted Minecraft, and downloaded it again from Minecraft.net.
I opened the file. Same window saying it was updating. Progress bar doesn't fully fill again, launcher opens again, black screen again.
I tried that a few more times, same problem.