That is a very healthy looking monstera! It is so beautiful. You bought a good one
Repot it. I see Arial roots in the soil and maybe some regular roots. Looks like yours is in a six pot? 8-10 inch pot will be fine. 8 inch may be good for now until Spring as its growing will be slower, but in spring put it in a bigger pot. My experience with monstera, pot size doesn't matter.
I bought mine in a 4 inch pot. January 2020. April 2020 I potted it in a 7 inch pot. I regret waiting this long to pot it. Poor thing was root bound. July 2020, it became root bound again so I put it in a 10 inch pot. It was growing like a weed. March 2021 the dog knocked it over and broke the pot.. it was still ok root wise in a 10 inch pot. I bought a cheap 12 inch plastic pot, and this monstera is still growing wild. Leaves and Arial roots everywhere. I really should trim it back.
If you put the monstera in an area that gets good sun, it will grow fast. Less sun, it will be slower. Mine sits right next to a picture window with lots of direct bright morning sun.