I'm seriously wondering if you can cause a seizure in a person without epilepsy. can you?

Yes: If multiple factors coincide like sleep deprivation, flashing lights, infection, electrolyte disorder, some food colouring, medication withdrawal, tec.

Absolutely: Any brain can be made to have a seizure if something bad enough happens to it. Epilepsy means a brain that has seizures under baseline conditions.

Certainly: In days long past it was an unfortunate treatment for depression. They took patients to a special room where they attached electrodes to their head & sent an electrical current through their brain, triggering a seizure. It was often done repeatedly. There are other ways to do it, including chronic sleep deprivation.