Is it possible to use AirDrop and Sidecar with a mac on a VPN?
Solution 1:
VPN can be set up to be compatible with both sidecar and airdrop.
The process of installing some VPN also can and will break these both if desired or they are targeted for blocking. The details matter of the network setup since macOS can have multiple networks assigned to one physical interface and software like VPN and admin control over networking can also block these transmissions.