Cannot change the default font size in mail when composing a mail.

The default mail font is Helvitica 12. I can change it every time I compose a new email but I can't change it on a permanent basis. I went into the settings and changed the font size for composed emails to 24 but every time I compose an email, it keeps going back to size 12 instead of 24. It still shows that it is set to 24 in the settings but it just won't change it when I try to compose a new email. How to I change it?

I am on OS 15.6.1