I know I have made another report under the same name, but it is a different issue.
When I open Minecraft Java Edition on any version past 1.12.2, the resolution is messed up in a way the set resolution is higher than that of the window size, causing all text and GUI to be a lot smaller and, while still playable, can be very annoying since all of the text is super small.
When I used the F3 Menu to see the display, it said 1708x960 when the window size itself was 854x480 (Which is what I set it to in the Minecraft Launcher).
But when I went back to 1.12.2, I entered the F3 Menu and the resolution said 854x960 which is also what the window size was.
SIDENOTE: When I entered full screen (Which I couldn't capture because of the area I was recording) the resolution in 1.13 was 2048x1152 (which is the setting I put it at in the settings) and when I set it to 2560x1440, the text becomes tiny again like the previous issue. I went to 1.12.2 and the Display said 2560x1440 and everything was good, not super tiny text.
I don't know why the Launcher isn't able to communicate the resolution (Not just the window size) to Minecraft Java Edition and I would like to have an explanation.
Video: https://youtu.be/VvJefN-JifE
UPDATE (8/19/18): I set the resolution in the launcher to 1708x960 and the text was very small still, I opened the F3 Menu and the Display said 3416x1920? I would like an explanation for why this is happening.
Unless you need to, don't change the resolution settings. Instead, go into the Display settings while in-game and change the GUI scale. I use a setting of "4" in 1.13.1.
The discrepancy between resolutions is because you have a High DPI display. Each pixel in software corresponds to 2 pixels (usually) in the display. If instead you treat it as a 1:1 ratio, everything is small.
The difference between 1.12 is to improve support of this type of display. You will need to change the GUI scale to make sure everything is the right size.
I've resolved this as Working as Intended as nothing you've said seems to contradict how it is supposed to work. If there is something specific that isn't working that I missed (and did not address above) please bring it to my attention.
Also, be aware that while OS X El Capitan is supported, it is nearly three years old.