My monstera doesn't look great after repotting - any advice?

Hi I was sent here from r/plantclinic - After repotting our monstera it isn't looking good, its previous pot was too small but now we aren't sure if this is too big. I'm fairly beginner at plant care but can try and give as much info as I can. Some info:

- It gets watered with a cup of water around once a week

- The soil used for repotting was just normal soil we found at the local shop, didn't look for monstera-friendly or similar