How can the recipient receive the funds while offline?”
The standard way as explained above is that the receiver must be online to actually be online to sign the transaction and also update the balance, this cannot be done while the Receiver is offline.
But now there are third part services that acts as intermediate between the receiver and sender, this third party service have nodes that are always online to recieve the coins on behalf of the receiver until he comes online and it’s then route to it.
An example as indicated in the thread link shared above is BlueWallet which has an always online node available to receive the coin and the update the balance themselves.