Lamaa - لَمى
Why is this word written in the Duolingo Font without an (visible) arabic m, but if you copy it in your browser search bar, the arabic m suddenly appears within the word?
That little, short line to the bottom right is the meem/m sound. It’s very common in some Arabic fonts.
it can mean two things : if there's a stress on the "m" it can mean "when", like in : "when he arrives ..." if it's like you wrote it "lamaa" it can also be pronounced as "limaa" which's from "li man" which means "for which/who" like in : "for who can hear me ..." if you talk about the curvy line linked to the "meem" it's only an "alef" but called "broke" or "maksoura" some feminin words (by their articles) have it instead of the usual alef
It's just a font issue. No worries.
Arabic letters sometimes can have various shapes according to calligraphy style and such. Just for the fun of it, google "Arabic calligraphy" and check the images.