Q.Mint Has White And Black Spots, And Looks Sick
At first, the white spots didn’t seem to be affecting the plant, But now, the leaves at the bottom look very sick and fall. The soil also seems to have white and orange mold. Actually, this plant is 5 months old, there are nearby plants that are two months old and seem to be doing well… Could this be a problem from the soil? I also see this tiny grey fly sometimes on them… But never spiders

Certified GKH Gardening Expert
I see spider mites! Well, I see the signs of their presence, rather.
Cut the mint back to just above ground level. It will grow right back. Make sure to dispose of the infected plant matter well away from the garden. Treat with a spider mite treatment, as well.
These articles will help:
https://www.gardeningknowhow.com/plant-problems/pests/insects/spider-mite-treatment.htm
https://www.gardeningknowhow.com/plant-problems/pests/insects/spider-mite-control.htm
This article will help you with mint care:
https://www.gardeningknowhow.com/edible/herbs/mint/how-to-grow-mint-plants-in-your-garden.htm