Theres a lot of confusion on this thread.
“Can Chometz be sold virtually? ”
No, a sale requires a kinyan, mot kinyanim require both parties (He might be able to do a chazaka on karka aquiring chometz with kinyan agav alone)
now, most of us don’t sell our chometz. We appoint the Rav to sell for us. That appointing of a Rav, pashtus DOES NOT require a kinyan, sure in most yeas we can be “mehader” to appoint the rav wit a kinyan, but as most poskim do’t require that , the Rav can be appointed virtually.