How to maintain 1 char at a time when holding down delete?
This is a 'feature' of Samsung's keyboard, default on Samsung android phones. I did look at Samsung's settings and did not see the ability to alter this. Use another keyboard to fix, which I did, such as Gboard by Google.

While I do like the ability quickly delete word by word also, that should be provided by a another key, not shared with the character by character key.