usability – Weekly report UI form: selection of multiple selection controls

Referring to omnifocus, use a switch as multi-selection.

In my experience, I am used to it (only my opinion, without research), but just below the multiple selection there is a single selection, and they look exactly the same:

Same control, different interaction:

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And on the mobile:

Observe how they should send comments to the user to ensure their selection on the switch:

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It seems you have room for a row of check boxes, and it makes it clearer:

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Question 1: Is it an error or a characteristic?

Regarding question number 1: if you have problems to know if it is an error or a characteristic, suppose that the user will not have more context than you.

You can try both options before making a decision.