The good news here is that you still have time since it would be much worse if you were standing in GE on your HS day and hitting this issue while trying to get a Boarding Group.
One more thing to try before running out to upgrade your iPhone. If you have memory hungry apps like FB or IG running go ahead and force quit them before opening
MDE and trying the VQ button.
Also there are some rather lower cost iPhone options out there vs an iPhone 11/Pro/Max, the cheapest might be the iPhone SE 2020 version. It is the same as an iPhone 8 in size and uses Touch vs FaceID on the X and later but has the speed of an iPhone 11 and will support the new iOS 14 this fall.
Link:
https://www.macrumors.com/roundup/iphone-se/
Dave