Pungent stink isn't a good sign. I would pull it out of that pot and discard all the smelly soil. Then repot the good stems. Toss that rotting stem. The rest looks okay to me. You can also take a cutting and root it in water now as a backup. When you repot, don't water for a few days.

I have a few of that type of peperomia. When I water them, I water the soil thoroughly letting all the excess water drain away. Then I let it dry completely before watering again which is on average once every 2 weeks. I live in a dry climate.

Thank you! Will try this 🙏🏼

i would return it.. this shouldnt happen after 3 weeks no matter why .... and i sure as heck wouldnt waste more money repotting it ...

especially if it was a good nursery ... ken

If you are in a cold winter area most house plants need to have watering cut way back when conditions change in fall (including the house becoming cooler inside). And peperomias such as the type you bought don't really like to be very wet at any time of the year.