To be seen on prints dust must be in the plane of focus of the lens.
A lens is focussed on the grain of a negative, so only dust in close proximity to it will be seen in the print. This can include either surface of the negative, the negative holder glasses and possibly the bottom surface of the condenser. Some enlargers use the bottom surface of the condenser as the top negative holder glass.
The light is focussed by the condenser, with the point of focus at the centre of the lens. while dust is always best removed from an optical system, unless it is focussed by the lens is almost never any sort of problem and can not be seen on a print.
In most cases Dust in a darkroom is only a problem if it is stirred up. If you spring clean a darkroom or enlarger, wait a few hours for the dust to settle before doing any work in it.
Never use a fan in a darkroom unless it is used for extraction. any vents for incoming air should be filtered.
Apart from damp dusting surfaces and washing the wet benches sinks and the floor. I only did a full spring clean once a year in my professional darkrooms, at that time every thing was stripped and thoroughly cleaned.
Print spotting was kept to a minimum, by ensuring negatives and carriers were scrupulously clean