Free text is allowed:

But you get a validation error (the normal one: "Validation Error – Required fields were missed or there was a validation error. Please scroll down to see details.") and when you scroll down, there are no errors. No * with a hint of what to fix. Nothing in server.log, nothing in the JS console.
@qqmyers says the free text stuff should be controlled by this (so not Dataverse code):
(that's the commit I tested on, by the way,
6055e9a).

Free text is allowed:
But you get a validation error (the normal one: "Validation Error – Required fields were missed or there was a validation error. Please scroll down to see details.") and when you scroll down, there are no errors. No * with a hint of what to fix. Nothing in server.log, nothing in the JS console.
@qqmyers says the free text stuff should be controlled by this (so not Dataverse code):
dataverse-external-vocab-support/scripts/skosmos.js
Line 208 in 6055e9a