The notch will exit with or without under screen tech. Apple is witnessing lower iPhone sales and the drop off occurred with the X line.
There are three primary reasons for the drop off in sales; 1) reaching point of saturation, 2) price versus value for the current offerings, and 3) a significant portion of iPhone buyers don't like the current form factor (notch).
Apple will deal with the above challenges. The three are somewhat interrelated. If Apple wants to open up new markets and get existing users to upgrade they must create value. Value will be created by either lowering prices or building something that excites the masses again. The X line did not do either of those, and thus, Apple is losing sales.
They will get ride of the notch one way or another. It is an abomination and they know it. They must excite people again or Android will continue to take over.