every time I click it, and exit out of the settings, I go back and check, and it changes back to the jar?
Mine hasn't worked in months, finally figured it out. TUTORIAL HERE:
incase you don't wanna do that or can't, here's the run.
1 ) Download (don't run) the file from:
https://bugs.mojang.com/browse/MCL-11993
2 ) Head over to twitch > settings > minecraft and at the top locate your save files. Remember this.
3 ) Open up finder, and locate your file, I used the "Find" Feature. You need to find the one called something like twitch, curse, etc.
4 ) When you look inside there should be something called minecraft > installs > game
5 ) Rename the file that is currently in there, then drag in the new file called "Launcher.Jar"
This should allow you to run it succesfully. Hope I helped!