Vibration from pedals at slightly higher speeds?

I’ve bought myself a new bike (BTwin Riverside 120) and I’ve taken it out for a couple of spins as of yet.. When speeds go above, say, 20-25 km/h (12-16 mph) (I’m giving a rough estimate based on what strava told me), there’s a distinct vibration of sorts that I feel when I’m pushing onto the pedal to propel the bike forward, and the lagging foot (I really don’t know the appropriate word, if any that exists) doesn’t feel any vibration even at high speeds. The vibration does not happen on speeds around 10 km/h (6mph) at all though.. What can be the reason for this? Is that normal?

Pardon me for being stupid but I’m just speculating here, can it be that the air cutting through my shoe soles is causing me to feel the vibration on my foot? (I may be pedalling wrong).

The saddle height is lower than what it needs to be for my height because the bike’s primary use is done by someone shorter than I. I say that because my foot is mostly not parallel to the ground when I’m pedalling, it’s mostly pointing up.