Unless there are instructions with the carrier a package is not delivered until safely into the property - by letter box, handed over etc
Carriers take it as risk that they put delivery targets on their staff that will involve packages left on doorsteps - should it go missing then a claim can be made
The contract with Royal Mail is with the sender (with ‘simple delivery’ the sender is eBay, with international eBay forwarding the onward sender after it is at the depot is eBay, in other cases the sender is the seller)
@pantalonmagique
If you have not already done so (eg you have only been messaging) raise it as a not received dispute
It is correct that the default view of eBay is that the tracking says it had been delivered and they would still payout to the seller. But it had not been successfully delivered and the photo is evidence of that.
The sender claims from Royal Mail (you can go to the Royal Mail compensation claim page but will not be able to process a claim without being the sender - and if you had enough details including despatch receipt, eBay transaction receipt etc, then a successful claim would payout to the sender)
With a dispute, based on the information available eBay would refund you.
If the seller is the sender then they need to claim compensation from Royal Mail
If eBay are the sender then they still payout to the seller and claim compensation directly
I have had this happen with a doorstep delivery, (though with Vinted)
As seller I received my payout and the buyer was refunded.