I'm going assume this isn't the best way to do this, but this works via a template edit.
Template:
member_view
Find:
Code:
<dd><xf:date time="$user.register_date" /></dd>
Replace With:
Code:
<dd>{{ date($user.register_date, 'F Y') }}</dd>
Results: Shows member's join Month and Day. (ex. June 2022)
You can use the PHP date formatting to adjust to your liking.