‎السلام عليكم ورحمة الله وبركاته Is it permissible for me to fast just on a Sunday? Or is it forbidden for me to fast on that day? And would there be any other singular days that i am not allowed to fast on (apart from the 2 Eids)? جزاك اللهُ خيرًا

The fatwa of Imam Ibn Baz is: There is no harm in fasting on a Saturday alone, whether it is an obligatory fast or a voluntary one. Saturday, Sunday, or Monday—fasting on any of these days is permissible. The only exception is Friday; it is not permissible to single it out for voluntary fasting. Friday specifically—the Messenger (peace be upon him) prohibited singling it out for fasting.