Sorry Private View is only supported for the responses table. That is when you are in View Responses Tab.
While in Design Tab, creating or editing the form, when changes made by one of the users are saved (manual or auto save), all the users will see the update.
Hope this answers your question,
Yes, we are only in the response table, but when one of us edit or filter, our screen jumps and we can see what filtering others are doing, so we have to always clear and re-enter into private view constantly.
>> but when one of us edit
Yes, even with Private View on you will see the editing of the other users.
Private View only works on filtering, sorting and rearraging and resizing columns.
>> or filter
If you have Private View on, you should not see the other users filtering/sorting and the other users should not see what you are filtering/sorting. If you don't have Private View on, you will see a warning dialog when one of the users (who does not have Private View on) tries to filter/sort the table. Or when you try to filter/sort, you will also see a warning dialog. These dialogs will ask you to either continue as is or to turn on Private View.
Note: you could also turn on/off Private View by going to View Responses Tab, app menu View / Private View. It will be good to inform your collaborators to turn it on while they are doing filtering/sorting for their personal view.
Please see this for more detailed information:
Do you have your responses published? Share/Publish Responses turned on?