So, some details on the difficulty I’m having with the three apps I use most extensively:
Google Calendar, Apple’s Notes, and Safari.
iPhone X, iOS 14.2.
Entering text in all three eventually grinds to a halt once a couple long paragraphs get entered. Key presses lag, typing becomes nearly impossible. Selecting and editing text, or simply placing the cursor becomes completely impossible.
gCal:
After a couple minutes of use, invariably the app stops responding to touches on the bottom third of the screen — in month view, you can only select events in the top three rows. Touches below do not register. Same goes for the schedule view, or the edit event view (changing calendars or colors or whatever).
Also disabled is the “+” button to add a new event.
NOT disabled in any of these above scenarios is the ability to swipe from the bottom to return to the home page. The touchscreen still works, just not in the affected apps.
In gCal,
Oddly, if you rotate your phone to landscape, the “right” third (bottom third) of the screen becomes responsive to touch again. This will even linger for a few moments if you select something, and then rotate back to portrait. But, alas, it won’t be long till it stops responding again.