Google Tag Manager: how to send a custom array to GTM so that a proper custom report can be built in Google Analytics

I would like to ask a question about GTM, but no ecommerce items array object, we hope to built a custom report with custom data sending to GTM and GA.
We have a multiple answer question in our survey, we want to sent the answers to GTM after getting feedback from customers. Finally, sending the data to GA to build a custom report.

I plan to format the data like this:

dataLayer.push({
            event: 'answer_survey_q2',
            answer_keys: ['ans_q2_1','ans_q2_3','ans_q2_5']
        });

However I don't know how to define a variable in GTM so that in GA I can build a report like:

Do you have any suggestion?

There are no array type currently or maybe not in the future either.

To achieve what you want :

1. Splits all the possible option to event parameter. There are only 50 event parameters quota in Free Version and 125 in GA360 version. So it's an option but no one will recommend this way.

2. Accept it as String type. So the value might be
   a, b, c
a
b

And you need to do the analyze in GoogleSheet or Excel on your own.