There isn’t any way to dynamically create fields through REST. The field need to either be exist in PHP, the DB or as a JSON file.
I suppose that you could create a field groups and save it as json in the acf-json folder of your theme https://www.advancedcustomfields.com/resources/local-json/
You might also be able to save the group as a serialized array as an option and then have an init function that reads in all of these options to dynamically add the groups on init… but the json method above would be a better choice.
As far as I know there aren’t any functions in ACF that can be called to create field groups the way that ACF does it.
