Nioro du Sahel Airport (NIX) does not have a lounge, but that is not the most important thing to know before flying here: Mali is currently under a strong government travel advisory, with many governments urging against all travel to the country due to terrorism, kidnapping, and civil unrest. Lounge questions are a distant second to that access reality, so check your government's current advisory before you plan any trip through Nioro du Sahel.
The advisory situation in Mali has been serious and sustained, covering large parts of the country including remote western regions near Nioro du Sahel, close to the border with Mauritania. Many governments' advisories rate travel here at their highest risk level, citing armed conflict, kidnapping risk, and limited consular support outside the capital. This is not a case where lounge amenities or airline status matter much: whether and how to travel to this part of Mali is the real question, and it deserves careful, current research.
Setting the advisory aside for a moment, Nioro du Sahel Airport itself is a small domestic airstrip, built for short local flights rather than any kind of transit hub, and it has no lounge, no day-pass option, and no card-network coverage to speak of. Bamako, Mali's capital, is home to the country's main international gateway, but even there, lounge access is a minor consideration next to the advisory picture affecting the whole country.
If travel to this region is unavoidable for your specific situation, prioritize current security guidance, local arrangements, and reliable local contacts over any lounge or comfort planning. Check your government's Mali travel advisory immediately before booking, and reconfirm it close to your travel date, since conditions can shift quickly. Airport comfort at Nioro du Sahel is the smallest part of the real picture here, and it should not factor into any real decision about this trip.