I've a modpack that relies on the default and expected 1024x768 for the custom main menu to be applied. For some reason, when i add the ModernFix mod, the game changes the resolution for a 16:9 smaller one, where the entire screen gets huge.

On the removal of ModernFix the game opens on the expected 1024x768 resolution inputed by the game laucher.

I've looked on the fixes mixins to find a potential cause, but wasn't sucessfull. Any idea on a possible fix?

Does it happen if you turn off mixin.bugfix.preserve_early_window_pos?

no, it does not! Thank you!

What launcher are you using that allows setting the resolution and the game actually respecting it? I thought this hasn't worked since 1.6 (i.e. for years).

Curseforge, it uses the default MC launcher

The next release of ModernFix will automatically disable this change if non-default (i.e. not 854x480) dimensions are specified for the game window by a launcher.