Well, right after posting I found a working solution. Doh!

Solution here, works great.

I use imput remapper for editing behavior of my input devices on my wayland gnome setup. I only changed the right super to behave like the left super and my legacy apple mouse to trigger super_L if squeeze it. I think it could help you as well with your problem, but you have to check, if it can remap key combinations to foreign signs, not so sure about that. https://github.com/sezanzeb/input-remapper

For Xorg there is something called xkb. I don't have experience in that. https://en.m.wikipedia.org/wiki/X_keyboard_extension

Another option -- if you only care about a US English layout for programming, have you considered just using a programming editor that has an input method friendly to that?

I kind of go the other way -- I'm in the US, and would like to have a way for inputting some things like Latin-1 stuff occasionally. Emacs has a lot of convenient input methods designed for this, inputting stuff on a US keyboard. And it seems almost certain to me -- there is no single standardized keyboard layout spanning Europe, so any European programmers must run into this -- that many programming editors must have application-level input support.

I used to use US international, but a few years back switched to Eurkey which is essentially just an upgraded/turbocharged version.

Might be too much for you, but I can't live without it nowadays!

I'm a Spanish speaker, and what I did was using sudo dpkg-reconfigure keyboard-configuration and assigned the right Alt key as the "compose" key: after pressing it I can press two characters I want to combine and it writes them out to the text output. I.e: to type á is Compose+'+a, to type ç is Compose+;+a, and so. That way I can use my US layout without losing special characters of ANY language