Thanks,
maybe I was unclear earlier. The checkboxes have nothing to do with the lookup field/dropdown list. I mentioned the checkboxes just to clarify the structure of the entire form, but that was unnecessary.
What I really do want is "click the dropdown, make multiple choices, save - just like a "normal" multi choice column". And I can't make that work. I have done as you suggested:
- I add the datacard to the form and the dropdown field is displayed
- Save, publish to Sharepoint
- But in the form, the dropdown menu shows Item 1, Item 2, Item 3, Item 4 … A workaround I found for this is to set Reset to true on the dropdopwn/DataCardValue. This does not help.

Before today, I also got an additional error, but now this seem to have disappeared: On some multi choice Lookups I get this error in the datacard Default (see image). I do not get this error on all multi choice. The error disappears when the Lookup column is set to single values only. When I try to save an item in the Sharepoint list, the form gives the error “Network error on using the function Patch: unknown error” (my translation). But as I mentioned, this error seems gone now.

