A month ago I did report this as an issue using the bug submission form:
Case # 11920817: Unreal Prerequisites Re-Install Every Launch on Steam Deck has been received
Thank you for your bug submission. We will review your case and will follow up if more information is needed or a ticket is created. In the event the issue you reported is scheduled for a future release or has known workarounds, you may not receive a follow-up message from our team.
I didn’t hear any further communication about the issue. Not sure if there are other avenues to get the issue acknowledged besides the bug report and forums.