Should we dust off the leaves of an indoor bonsai with a dry sopalin by gently massaging each leaf towards its ends and then towards the outside?
Google tells me that 'sopalin' means kitchen paper or kitchen paper roll. No, don't use that, its too rough. The best thing to use is either a paintbrush (specially a larger paint brush of the type that children might use to do a painting) or a blusher brush, or any type of brush used for make up for the face. I suppose an ordinary paintbrush intended to paint a door frame or something might work, provided its fairly soft and has long bristles, but brushes intended for use on the face are the softest of all. Image in this link of a blusher brush https://www.byrdie.com/best-blush-brushes-4586784 to give you the general idea.
In regard to bacteria, there's no more bacteria in the dust on a plant than there is in the dust on your sideboard or shelving in your home, so that's not a problem, though if there's an excessive amount of dust, you might try not to breathe it in to avoid airway irritation. Have the vacuum cleaner at the ready if there's lot of dust - that will all end up on the floor.
If the dust has been there a long time, it may not simply brush off, so try with the brush first, then you might have to resort to using a soft, dampened cloth to carefully clean the leaves.