An electron is just an excitation of the electron field, a vast probabilistic something that's ever-present everywhere in the universe, with a different complex-number amplitude (not observable directly) at each and every point. Sometimes that vagaries of its ever-changing amplitudes cause it to locally coalesce into something that looks like an individual electron if you squint at it in the right manner, and that vision persists until a strong enough interaction with another vast and nebulous field shatters the illusion, at least in the tiny corner of the probabilistic multiverse your local version of your consciousness brazenly imagines to be the objective reality. What kind of existence is that?
An existence that mistakenly took fundamental reality to consist of point particles instead of fields. But we still found out about fields and quantum mechanics.
We don't know that fields are real. We just know that the mathematical language of fields is the most convenient and concise to describe the experimental results we see.
As a starting pint, the magnetic field can be shown to be real with metal filings. Whether fields are the fundamental building block is another matter.
(Well, the only kind on offer, really.)