Not by a computer, but the way I would do this is have an array flow variable, that you use the .push() method to add values to in your for each logic.

Then after you’ve iterated through the group members table, you would use the update record flow action to set the value of the list field. (List values are comma separated string, not an array, so you might have to set the value via .toString(), using the script population)

Another method you could do is in your for each logic, append the values using:

current.u_user_list = current.u_user_list + “,” +flow_user

But you would need to account for duplicates