@Anonymous using "Respond to a PowerApp or Flow" action you cant return an array, so i would suggest to change the type of variable to string. And instead of Set Variable use "Append to string variable" action and use concat expression to concat values of id, name surname, age, location, etc, example expression as below:
concat(items('Apply_to_each')?['ID'],', ',items('Apply_to_each')?['Title'],', ',items('Apply_to_each')?['Name'])
See how actions will be added in flow in screenshot below

Are you using filter query on Get Items to get specific item from list?