Background / History

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. 

Fix for the New Angular UI in 2sxc 10

1. Go to App-Data and enter the fields of the ContentType SubmitType.
2. Change the input-type to Dropdown from Query 
3. Now go to the field settings and first set the query to Eav.Queries.Global.ContentTypes. Make sure you first click the TT character so you can type something that isn't provided in the dropdown. Otherwise your selection will not work, as the UI thinks you're searching. 
4. Now the other dropdows will let you pick the values as needed - configure it to be like this: 
5.   Save - and try editing the form, you should be good to go.