When we created Mobius Forms 1.0 there was a critical feature missing in 2sxc - a dropdown to pick content-types. So we added a hidden input-type called contenttype to select this. It was never official, but allowed us to create Mobius as it is. The special field was used in SubmitType Content-Type on the field ContentType.
In 2sxc 9.x we then introduced the string-from-query-dropdown and created system queries which would return the Content Types needed. We then had an official way to do it, but forgot that Mobius still had this secret feature in use. Later when we created the Angular 10 Edit-UI for 2sxc 10 we didn't create the secret input-type any more, so one of the configuration dialogs only works with the old UI. Or we recommend you reconfigure the field like this.
2sxc - Content Management for DNN & Oqtane