I had a problem like that years ago finally resolved to be a bad connection of the
12VDC at a firewall connector to the cabin. Your situation requires that you
note carefully what things are, and are not, working when the car quits.

Start by servicing the battery cables and grounds in the engine compartment.
If the starter spins fast without lugging and growling then pay particular attention to the piggy back red +DC wires on the battery, and the 30 Amp cable to
the ignition switch, Look for loose or corroded connections where the cables
are crimped into the terminal ends.

It's hard to troubleshoot flaky battery cables, since they can test out OK with
low current, but suddenly quit under load.

Loss of a critical ground path to the intake manifold could disable the injectors
and leave everything else on, That's why you want to note in detail exactly
what quits and what doesn't, to aid diagnosis.

Bill