Hi Antoine,
Correct, unstable_createFieldAsync
doesn’t support creating formula fields at the moment, and there is no other programmatic way to create a formula field. You would need the user to create the field manually (though you could provide the formula text for them to copy + paste in to the field).
Would love to hear more details about your use case for creating formula fields in this block. We’re keeping track of requests for extensions to these “metadata writes” APIs and I’ll note down your use case!
Thank you,
Emma