It’s also not handy to reach the mark-up characters from a touch keyboard. And if you are adding backticks and asterisks to a markup bar, you might as well just add bold and italics to the markup bar.
This varies a bit by touch keyboard. The standard iPhone keyboard is particularly bad at this while the AOSP and Google keyboards on Android aren't so bad.
Joplin, the notes app I've been using lately does have a markup bar with those features.