It is possible that in select_multiple you can select all the options at once or give it a condition.
For example: we have a geography test, which asks
What countries are from Latin America?
7. Select all of the above
Select_multiple country Which countries are from Latin America?
I want to select number 7 to select all the previous ones, or in its defect indicate by means of a conditioner that I select everything.
I don't know if there is any method
You can default a multiple choice to already show items as selected in the design tab, but in the scenario of a quiz this defeats the purpose of that function. I would suggest checking Survey123 Connect on the desktop, it has a wider range of functions and tools than regular Survvey123. If anyone else doesn't find a solution I would recommend putting this into the ideas page for Survey123 as a new feature you would like to see because I would like to see it as well. ;)
Hope this helps some, best regards,