Use Durbond90, or if you are not experienced with plaster reapir yet, Easysand90.

These are 'setting type' joint compounds that come as a powder and are mixed with water.
Mix them as thick as peanut butter for larger cracks, a little thinner for smaller cracks.
The less water you use the less shrinkage on setting.
They do not harden by drying like pre-mixed mud.

The number is the approximate hardening time in minutes.
Both longer (240 Min) and shorter (20 min) with some additional steps available.

Durabond is as hard as plaster and cannot be sanded well at all, so be careful.

Unless the crack is taped, it will probably continue to show up.
Ron

Bondo is half benzoyl peroxide and is highly flammable, explosive, toxic, and may act as a mutagen. Halfwit mechanics love to put a lighter to the dust. But it is an effective horsehair plaster patching material if you take precautions.

Here is a link that might be useful: yes it burns

"Bondo is half benzoyl peroxide"

The benzoyl peroxide is the catalyst that initiates the hardening reaction.

The material is styrene monomer with additional fillers.

Benzoyl peroxide at low concentrations (10%) is used for acne medicine.

Powdered styrene is very flammable.