https://paste.ee/p/7lR09
From line 860 onwards is from what I'm told an Apple exclusive issue about stretching windows. This issue might be similar to the other mac related crash? #142 (comment)

Mac with Mojave 10.14.6
Current Java x64 build 281
minecraft 1.16.5
fancy menu 2.0.5
konkrete 1.1.5
Forge 36.1.0

from the Engineers Life 2 modpack.

I. Hate. macOS.
I don't even stretch/resize the window and everything happens in the frickin main thread. This error is so random, I don't get it. I literally just use the same method MC uses to set window icons and titles.

Thank you for telling me, but I'm not sure if I can fix this, because I have no clue why this even (still) happens.

Does it happen everytime you try to start the game?
Problem is, I don't really have access to a Mac with macOS 10.14+, so I can't even debug it..
It works fine for me on 10.13 (and probably on most other Macs too, because there would be much more reports about this if it would happen to every macOS user.

And the game starts normally when you remove FancyMenu?
If yes, can you try to load the game with only FancyMenu and Konkrete installed, please?

It might be a Mojave issue because it removed 32-bit support? I don't know.
Yes, the game starts normally when I remove fancymenu and konkrete, BUT
if I do a fresh instance of 1.16.5 with just fancymenu and konkrete, nothing else, it loads to the main screen.

Hmm, interesting. And if you add the other mods to this new instance (+ fm and konkrete), does it start then? Or is it crashing again? Maybe a combination of FancyMenu and other mods is causing it.

But I think that’s really a random error and not really caused by FM, but MC + macOS in general.

Closed because I wasn't able to reproduce this, I'm very sorry.