I know it's been a while since this was posted, so not sure if you ever found the solution but was struggling with the same issue for a while and was such a pain trying to find a fix...
If you want to show the Medial Pool and Effects stacked for Vertical Video, you'll have to disable "Use Optimized UI layouts for vertical video" under User Preferences > UI settings - see below:

- Screenshot 2025-05-31 at 06.06.25.png (40.18 KiB) Viewed 582 times
Vertical Video UI with Optimized UI enabled:

- Screenshot 2025-05-31 at 06.07.38.png (648.03 KiB) Viewed 582 times
Vertical Video UI with Optimized UI disabled:

- Screenshot 2025-05-31 at 06.10.43.png (621.79 KiB) Viewed 582 times
Hope this helps.