Thank you. I post and reply all on my phone, so I’ll look into it.You can apply strike through to your text by highlighting it and pressing CTRL+S.
Alternatively, you'll notice there is a small menu bar while editing/replying which contains text formatting options. If you look just right of the paint palette icon, there is a button which looks like three dots in a vertical row. If you press this, it will drop down additional (less common) options- one of which is striking.