The Arabic font in Manjaro KDE 18 isn't readable at all. It looks like a calligraphy font than a standard reading one. It is not meant for daily uses.
Reading (at an adult level at least) is not about identifying the order and shape of letters, but rather pattern recognizing a combination of letters semi-instantly give the context of the sentence. Change the default font to "noto naskh arabic font" or any other font that is good for daily uses.