On my sharepoint online list, and the associated form for adding a new item, there is a field/column which is aligned to a term set.
In the standard form, if the item the user wants to input is not in the term set, they can click on the tags on the form and it will open the term set tree, where they can see all terms in that set, and also add one if it is not present.
Is there a way to add this function to a powerapps form??
As of now if your list or library has a managed meta-data column type from SharePoint, our Form Control will expose the Managed Metadata Column as a Combo Box. (Try creating an app from data where a column in a list is set to a node in the Managed Metadata to see how this works.) This would provide a similar experience in that as they type in the combo box it will search through the tags for relevant choices.
Let me know if this is sufficient for your business scenario, or whether you'd like to achieve something outside of this current state please.