Hey @Dylan P.
Thanks for asking a really great question on flow notifications.
Unfortunately the dynamic email variable will only work in the content section of the notification. The “Send To” and “From / Reply-to” fields have to contain an active email address. This is really intended for internal teams to communicate more effectively. For example, notifying your customer experience team when someone leaves a detractor NPS score, or alerting your sales team when someone is added to a wholesale or VIP list. The “From / Reply-to” allows the other teams to reach back out to you if there is any additional needs.
Hope this helps!