init.lua

hs.hotkey.bind({}, "§", function() hs.eventtap.keyStroke({}, "`") end )
hs.hotkey.bind({ "cmd" }, "§", function() hs.eventtap.keyStroke({ "cmd" }, "`") end )
hs.hotkey.bind({ "shift" }, "§", function() hs.eventtap.keyStroke({ "shift" }, "`") end )
hs.hotkey.bind({ "cmd", "shift" }, "§", function() hs.eventtap.keyStroke({ "cmd", "shift" }, "`") end )

I exactly want the same behavior you describe (shift + backtick producing ~). It doesn't works and still print ±.

It looks like hs.hotkey.bind({ "shift" }, "§", function() hs.eventtap.keyStroke({ "shift" }, "`") end ) doesn't behave well for me.

@ghigt I am sorry to hear that. It works fine for me. You can also play with some debugging and see what's going on.
I used this (paste on the console and once you are done, just reload config) it might help identify the problem:

local function keyCallback(event)
    hs.alert(hs.keycodes.map[event:getKeyCode()])
end

keyWatcher = hs.eventtap.new({ hs.eventtap.event.types.keyDown }, keyCallback)
keyWatcher:start()

As for reference, after pasting that on the console and pressing shift+§ I get 2 notifications: one with § and another with backtick.

After testing with your debug, I finally saw that the ~ worked out of the MacOS Terminal app (it works fine with iTerm though). So I don't know why but it works everywhere except in the app I want to use it 😄

Big thanks for your help!!

The sudo hdutil stopped working for me as of today (macos 15.2) with the following error:

$ sudo hidutil property --set '{"UserKeyMapping": [{"HIDKeyboardModifierMappingSrc": 0x700000064, "HIDKeyboardModifierMappingDst": 0x700000035}]}'

Attempt to remap alphanumerics / special characters. If setting fails, ensure Terminal has input monitoring permissions.

This Hammerspoon config works and saved my day! Thank you! 🎉

@VojtechVitek hdutil shouldn't need sudo after MacOS 15.2 update any more. Did you try without?

$ hidutil property --set '{"UserKeyMapping": [{"HIDKeyboardModifierMappingSrc": 0x700000064, "HIDKeyboardModifierMappingDst": 0x700000035}]}'
Attempt to remap alphanumerics / special characters. If setting fails, ensure Terminal has input monitoring permissions.

Add Terminal to your settings : https://support.apple.com/guide/mac-help/control-access-to-input-monitoring-on-mac-mchl4cedafb6/mac

My current MacBook has the American keyboard layout, so I don't need this anymore, however, it is important to keep this updated for those who need it.

Thank you @ghigt and @VojtechVitek. I updated the first comment to reflect your findings.