AirTags would be a terrible method of tracking a vehicle given that they warn any phone in the vicinity they are nearby when it looks like they are tracking.
There are products specifically designed for vehicle tracking however and that would be far more fit for purpose
Any security worth their salt would be conducting regular bug sweeps of vehicles and modifying regular routes to avoid routines where possible even if you got close enough to the vehicle to install the tracker the likely hood it would be in situ long enough to understand a regular routine is minimal. Then you’ve tipped off security that someone is tracking him so now they are on high alert.
Elon is likely travelling in an explosive resistant vehicle. Protection against under vehicle explosives is relatively common.
How would you detonate an explosive? Depending on the threat model the vehicle/nearby vehicles can be equipped with signal jammers meaning you need a hard wired detonator.
Shooting a plane out of the sky? No thanks. The Russians just gave you a very real and practical alternative recently. Just install a small explosive on the plane.
A couple of notes: