Use OpenCore Legacy Patcher(r/OpenCoreLegacyPatcher or [site](https://dortania.github.io/OpenCore-Legacy-Patcher/)) to install a newer version of MacOS that supports Universal Control. I have Sonoma running on Macbook Air 2012 and Macbook Pro 2017.
I've never done it on a headless Macbook. You might need something like [weak fridge magnet](https://www.reddit.com/r/techsupportmacgyver/comments/gizjxj/used_a_very_weak_fridge_magnet_and_some_masking/) to force the display to go external during setup.
The 2014 MBA doesn't support Universal Control. [https://support.apple.com/en-gb/102459](https://support.apple.com/en-gb/102459)
it should be patchable, there are kexts that enable it and sidecar
Use OpenCore Legacy Patcher(r/OpenCoreLegacyPatcher or [site](https://dortania.github.io/OpenCore-Legacy-Patcher/)) to install a newer version of MacOS that supports Universal Control. I have Sonoma running on Macbook Air 2012 and Macbook Pro 2017. I've never done it on a headless Macbook. You might need something like [weak fridge magnet](https://www.reddit.com/r/techsupportmacgyver/comments/gizjxj/used_a_very_weak_fridge_magnet_and_some_masking/) to force the display to go external during setup.