EDIT: Solved! Check this comment!

I use a keyboard with an american layout. I find it much better for coding and actually love this keyboard to pieces. However, I still need to write in portuguese.

The dead keys in Microsoft Windows worked perfectly for me but the Linux ones do not. Some characters are not available and are replaced by characters that don't exist in the portuguese language.

In X11 I fixed this by using an .XCompose file with the keybinds just like in Windows. Source here, it works perfectly.

In Wayland, the .XCompose file works for pretty much all apps. Firefox is fine, kitty is fine, Vivaldi is fine. Unfortunately electron apps with the --ozone-platform-hint=wayland ignores the .XCompose file and I get the default keybinds. Since I own an nvidia card I really need these flags, otherwise the electron apps will aggressively flicker and/or eat letters while I'm typing.

I've searched far and wide, there are several open bugs in chromium, electron and wayland repositories. Everyone seems to be pointing fingers at each other for years and no workaround to make .XCompose work seems to be available.

I'm wondering if there is an alternative way to customize the dead keys under Wayland. Thanks in advance.