I have a dozen regularly typed words that I have had to set up string replacements for (in General -> Keyboard -> Text Replacement) to work around recorrect the autocorrect.

It used to be possible to tell autocorrect to ignore certain words and add them to the system dictionary (by typing the word, having jt autocorrected, hutting backspace and fixing the autocorrected word, and repeating the process 2 or 3 times), but that inexplicably stopped working for me a few years ago.