@mk@oracle.skilledtests.com That was only "one way", as I wrote. :-)
Another way is just like you expected:
1. Start creating new message by pressing "envelope+" on an Action bar.
2. Now, as a message Editor is visible, another button appears on that Action bar: "attach+". See it on my picture, attached to this message. (That "Attach an image" menu item may be hidden under "Overflow" button ("three dots").
3. Tap on that "Attach" button and select picture normally.
4. Continue typing your message, if necessary. Then tap "Send". https://loadaverage.org/attachment/2780547