Seems like there’s no trade off to over-engineering health and safety in the context. N100 would be adequate but the P100 additionally provides a broader spectrum of air pollution exposure reduction which in the context of infection control helps protect the mucosal barriers from damage and preserves immune fitness, preventing T-cell depletion caused by inhalation of vehicular pollution and industrial/commercial combustion emissions, smoke, and so on.

P100 is the common designation in most uses you saw pre-pandemic, i.e. Asbestos removal, and the GP is referring to a legacy mask.

P100 is much easier to find than N100