Hi. The behavior you describe is expected. The Survey123 webhook payload models records within a repeat as an array. This is the case because in a repeat you may have one or more records. In Microsoft Power Automate, the standard behavior to handle an array is t add an 'Apply to each' block. Using the Initialize variable and append to variable modules will let you aggregate information from your array.
Overall, your workflow could look as follows:
Note that I added an Initialize Variable before the Apply to each. Within the Apply to each bock you can use the Append to variable module to aggregate data from your repeat and ultimately reference that variable within your email to bring all the aggregated repeat data into your email content.