This opener has two separate coil springs around the shaft that has a cable pulley on each end.
The right hand coil spring is broken... must have broken when the door was closed and everything still.
The left hand coil spring is still good.

It is a massive double car width single door.
18 feet wide. 6 foot 10 inch tall.

I cannot lift it with the chain release lever pulled.
I have manually lifted the door easily when both coil springs were providing help.

If I climb on top of the van and sit,
I can use the 18 inch leverage of a solid steel tension adjustment bar to lift the door about 2 inches off the ground,
but the weight is too much for one arm to hold while the other arm would get a 2nd bar in the hub on the shaft to hold against the wall.

I have called the local Liftmaster dealership.
They are “booked solid” for the day
but since the vehicle is trapped inside the the garage they say they will try to have an employee come over if only to get the vehicle outside the garage.