They are called gland dots, come in red, orange, etc., or colorless. Are probably sessile trichomes. Plectranthus are often covered with trichomes which come in several forms, often hair-like. Red ones on the upper surface are new to me, and are sometimes on the lower leaf surface, or on the calyx, etc. Do you have a name for the plant in your excellent photos?

Red gland-dots on the leaf underside of P. australis.

Thank you! Thats so interesting, I thought there might have been something wrong with it. I believe it's a variegated mint leaf plectranthus

There are several Plectranthus called mint leaf causing some difficulty. There are photos which look much like yours called P. discolor, but it is difficult to see if there are red dot gland spots which show up so well in your photos. Another 'mint leaf' is P. madagascariensis,, one which is widely sold, but it is difficult to tell if that is what you have. If you get it to flower, identification would be easier. In any case, you have a nice plant, and you have me looking for gland dots on my Plectranthus.