Nasotracheal suctioning is used to clear the nose and throat - often in people with obstructive airway diseases or illnesses, but only by trained personnel.
Lung tissues are remote from the nose, sufficient suction to remove mucus would surely damage the lungs and airway.
Intubation through the nose and airway are used in emergencies to reinflate lungs or attach a respirator, and in some cases to suction out blood or excessive fluid, but these procedures are done by trained professionals.

If they are talking about NTS, I agree it is too risky to attempt. Sterile gloves and suction catheters are used to avoid introducing bacteria.

I doubt that’s what they mean since it triggers cough reflex and I can’t imagine would be possible on your own.
I wonder if it’s nasal or post nasal drainage which would be like aspirating mucus with a bulb syringe, but using a catheter. If there is much suction, I’d think bloody noses would be a risk.