Same issue, I've used Airdrop on this Mac Studio hundreds of times to upload photos ... now, after the latest Sonoma upgrade (14.4.1 to 14.5) it doesn't work. I've done the defaults write to com.apple.mDNSResponder.plist thing, I'm not using a VPN, and I've looked for other computers with a similar name in my AirDrop list of devices (all various 'fixes' that people have mentioned in this thread), but none of that worked or was applicable.
I did monitor my Console while trying to send something and found some timeout errors, but don't know how to interpret them:
Failed to resolve peer device 'IDS 599E8B32, Nm 'Mac Studio', Md 'Mac14,13', SF 0x80000A0302 < BLE DuetSync WiFiP2P Friend Owner AirDropUsable >, DFl 0x1 < Info >, AcLv = Screen (7)'. Error - Error Domain=RPErrorDomain Code=-6722 "kTimeoutErr (Request timed out before send)" UserInfo={cuErrorMsg=Request timed out before send, NSLocalizedDescription=kTimeoutErr (Request timed out before send), cuErrorDesc=kTimeoutErr (Request timed out before send)}
Just before that is:
### Session start send failed: Service com.apple.sharingd.AirDrop, PeerID 599E8B32-B55D-4785-A0ED-9AD550D9165A, CSID 0x6D01D41B, kTimeoutErr (Request timed out before send)
and before that (from the AirDrop process):
Failed to log access with error: access=<private>, error=Error Domain=NSCocoaErrorDomain Code=4097 "connection to service with pid 250 named com.apple.privacyaccountingd" UserInfo={NSDebugDescription=connection to service with pid 250 named com.apple.privacyaccountingd}
and before that, three things, all from the Airdrop process, related to CAML:
CAML error:47: `o' element must have `type' attribute
CAML error:47: Unknown value element `LKEventHandler'
CAML error:47: No such class `LKEventHandler'