Why the mim is not written ? Is it due to some ligature glyph specific to ل then م ?
the mim is written in the word ل م ى .. لَمى
mim alone is م and mim between other characters is ـمـ
Thank for your answer ! It was a font issue, as identified in the comment below.
I think you have a font issue. It's OK. Notice a little stroke under the base of لـ - this is Mim. If you can change the font you might be able to see the difference.
Indeed, a font issue. On Duolingo desktop and app, the mim disappears, but in the mail notif (gmail, desktop or app) as well as when I copy paste in Google Translate, the mim is well there.
It is a style of calligraphy by the way and not a real issue but I had to address it as a "font issue"
For the fun of it, check Google Image search for "Arabic calligraphy" to see variants of shapes for the letters in artistic suit.