Combine responses from a multiselect question into a string variable

I’d like to create a string variable that collates all of the responses chosen in a multi select question. For example, for this multi-select question:
G7. What documents do you have for this parcel?
1. Title of ownership
2. Lease
3. Inheritance contract
4. Etc.

I want to create a string variable that would store something like “Title or ownership, inheritance contract” if they chose options 1 and 3.

I see this syntax for combining List question responses into one variable : String.Join(",", G7.Select(x=>x.Item2)) So I think I am looking for something like this but for multi-select questions.

Is this possible, and if so, how?

Thanks in advance.

You cannot use multi-select titles in this way.

In most of the cases you should not use text values in conditions(variables) but use substitutions to display referenced questions.
But multi-select question is not supported in substitutions as well.

Define string variable S as:

   g7.ContainsAny(1) ? "Title of ownership," : "" 
  + g7.ContainsAny(2) ? "Lease," : "" 
  + g7.ContainsAny(3) ? "Inheritance contract," : "" + ...

You will need to trim the trailing comma yourself. Then display S where you need it.

This solution has a number of vulnerabilities, which is why it is impossible to recommend it without knowing your context. Perhaps showing at least the section where the question is posed can yield better suggestions.