So, how should I approach this?
It's up to the buyer to oen a case under eBaysd money back guarantee.
eBay will review the tracking record. If the tracking confirms delivery to the correct address they will find in your favour. We often hear of cases where eBay has accepted delivery photos taken in common areas of shared buildings. (For that matter, we often hear of eBay accepting delivery photos which the buyer claims are not even of their house!)
As you are a private seller I imagine this was sent using eBay's simple delivery? If so, if the buyer finds in the buyer's favour they will refund them themselves. It won't be charged to you.
If the buyer leaves bad feedback because you used Evri through eBay's Simple Delivery this would probably be removed if you contact eBay customer support.