Thank you Evan for the advice.
I successfully compiled MagicCombo using the format inside this upgrade notes.
The physical keys assigned to MagicCombo activate together with the assigned action as discussed inside this thread.
Due to that, I decided not to use MagicCombo for now.
I understand it takes a lot of effort from the Maintainers/Contributors to get MagicCombo to work the same way QMK’s Combo does.
Nevertheless, I can still utilize other Kaleidoscope great features to bring out the greatness of Atreus, e.g. Qukeys, TapDance, etc.