> complete keyboard remapping such that macos keybindings work everywhere
I also use a customized layout (mostly international English with shortcuts for German Umlauts and Y and Z remapped to eachother). It definitely works in most modern Linux desktops to use a "custom keyboard layout" like described here. There are many guides which are outdated on the topic. It's a hack and also not super simple to execute (you only need to do it once) but it is persistent and system-wide in all programs at least: