Does my Monstera have a fungal infection? Browning under one leaf

Hi all! I'm a new plant owner and recently bought a Monstera a few days ago. I've since noticed some browning on the underside of one of the leaves. None of the other leaves have this. I've also noticed some browning on the plant stem. I'm wondering if this is a fungal infection or something else I should be worried about? I'm a beginner to identifying pests and issues, so any help would be greatly appreciated. Thank you!!

Note: I should say that the leaf that has the browning underneath is also slightly damp/soft to touch as opposed to the other leaves.