Literally the whole question is in the title. How do I receive iMessages from a certain person in scriptable? Or is that not possible?
Not possible, you are correct
Technically there’s a way but not without caveats.
You can create a Personal Automation in Shortcuts for when you receive a message from the person and where the message contains a particular keyword or phrase (caveat 1). The keyword or phrase is required, and only one can be assigned. You can create multiple automations if you prefer.
The automation can grab the whole message using the
Shortcut Input magic variable.
You can then pass that message to Scriptable.
Caveat 2: You’ll need to manually tap the automation notification for it to run. This trigger does not have the
Ask Before Running toggle.