I can't be bothered to look through all the topics listed on the forum to see if this has been reported before. There are just too many topics. So here it is!
I run Mac OS Mojave version 10.14.2 and have just started using Musescore 3.
If I highlight a word, right click and select "Edit Element", the program may or may not quit unexpectedly when using the arrow keys to navigate through the word or the backspace key to delete letters from the right. It doesn't happen every time and I've not yet worked out the sequence that causes it to happen. I haven't found the same issue when deleting a letter from the left using fn + backspace.