The Numina are the gods of NUM, who govern the natural and unnatural phenomena of the universe. There are hundreds if not thousands of Numina. Generally, these are divided into the Kohr Ah, called the star gods, the Ugara, called the earth gods, and the Adrasta, which are called the gods of war, or the gods of man. Apart from these are Vanu Mar and Korro Khaitan.
With the exception of priests, it is extremely unusual to find someone in NUM who reveres only a single deity. You are as likely to find someone who eats only oats, or only wears green. It does stand to reason that a midwife would make offerings to Anasara (goddess of families and fertility) more frequently than to Skudra (god of smiths and of scholars), but the Numina all have different areas of influence, and it would make no sense whatever for a typical person (a non-priest) to reject all others in favor of a single deity.
Priests are another matter. Priests do devote themselves to a single deity, or to a small group of related deities, and they might place themselves in opposition to priests of an opposing deity. But a priest of Anasara would still pray to Azif when trying to light the hearth on a cold winter morning.
To put it another way, someone who works for one brewery might refuse to drink the beer from a competing brewery, but they still drink water, and fruit juice, and milk, and wine, and cough syrup, and so on.