Yes, they are both privacy friendly OS with microG preinstalled to replace Google services. But they're not based on the same project : IodéOS is based on LineageOS (like /e/OS) while Calyx uses AOSP.

It's not a huge difference but in my experience after switching from Calyx to Iodé, some applications wouldn't work anymore, mainly banking apps.

It does : https://iode.tech/iodeos-official-supported-devices/

I hope there will be a good Linux phone in a few years that I can switch to. Would be great with it was compatible with the latest Fairphone by then, for a true FOSS and ethical phone.

Pizzaius