Reason
During my testing, I decided to test the custom keyboard and you wouldn’t believe what I found out. When you try to long press on the delete/backspace key, nothing happens.
Idea
I propose that the custom keyboard implements a similar delete behavior as the built-in keyboard with one caveat, instead of the long press deleting more and more depending on how long you hold the key, it deletes at a normal pace. There are some note taking apps that incorporate a similar behavior and it makes me happy.