Adding an artist with a name already in use is not intuitive. See https://community.metabrainz.org/t/disambiguation-field-wont-accept-any-input/667219

Primarily, the issue is that the disambiguation field's state does not refresh correctly.

1. Go to https://beta.musicbrainz.org/artist/create
2. Enter a name already in use; e.g., "test"
3. Leave the sort name blank.
4. The disambiguation field will highlight in red and add the label "Required field."
5. Filling in the disambiguation field will neither clear the red highlighting nor the "Required field." label.

This behavior differs from the following alternative scenarios:

A) after step 5, refresh the page

B) after step 5, change the name