When composing a post while logged in on embracing.space, the M icon
does not show. To be able to test directly on this instance, you'd
need an account. If you want one, consider asking
On Pleroma instances (fedi.absturztau.be and obese.cat) the icon does
work as you described.
The attached screenshot is of the compose box of Husky while on embracing.space.
(Repost because the first attempt was rejected by the mailing list
because Gmail put HTML in it again)