I've seen this issue before in searching, but wanted to see if there are any new solutions / ideas out there.
I've made a solution containing a Power App and a few Flows. Nothing too crazy. Using the Approval system along the way. When an approval starts, it takes at least 15 minutes for the initial email to get to the Approver. If using the Approvals app for Teams or the Approvals dashboard, everything is fast as it should be. Going to test out Adaptive cards next, and I assume they will be fast as well.
But users still live and die by Outlook. Are there any updates on why that initial approval email takes such a long time?