EDIT:
Actually, my issue is NOT resolved. It works when I click the "Resend Receipt" button in admin, but it does NOT work when the customer first places the order. I feel like this must be some sort of permissions error, but I already enabled the "View own webform submission" permission.
I also enabled "Anonymous" and "Authenticated" in Settings > Access > VIEW OWN SUBMISSIONS for this webform, but that made no difference either.
I then tried placing an order as admin, thinking that would clearly show whether it is a permissions issue. The order email for the admin user's order also did not include the content from the view. So it is apparently not a role/permissions issue either.
Anyone have any ideas on how to resolve?
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Original (not-working) fix:
Issue resolved. I installed the Twig Tweak module, and then added this to my order email template file:
{{ drupal_view('my_view_name', 'block_1', order_entity.getOrderId) }}
If I had used the Order Number as the contextual filter instead of the Order ID, then I believe the code would look like this:
{{ drupal_view('my_view_name', 'block_1', order_entity.getOrderNumber) }}