Small transformer, yes. Not the big trunk line ones though. Mineral oil simply isnt up to that challenge.
Point, which is why many modern GSU transformers at the plants use Mineral oil inundated pressboard, which is basically made by taking unbleached kraft paper pulp and poly(4-methylpentene-1) (which is another fairly common material, we use it in pretty much all of our microwaves safe plastic dishes, and at least some is used in the vast majority of electronics, even things as simple as LED's), grinding them up and laminating them together with the oils. Note: I'm literally taking all this data off of producer pdf's such as
this.
Yes, there are more and more of those large transformers today that are using metamaterials and whatnot for their designs. But often this isn't because they
can't use the simpler oil-based designs (or oil-pressboard designs), but rather because the fancier materials are
safer and allow for more efficient designs.
As for the Quebec blackout, I'd like to note that the breakers did what they were supposed to do, and while a blackout happened, very little real damage was caused (which is why it only lasted 9 hours), and we've spent the time since then upgrading safeguards and learning more about how to manage power in such an event, albeit slowly. Yes, should a big storm like the Carrington-level one hit us we would be talking trillions of dollars being lost, and possibly some places being without power for months or even a few years as we repair the grid (it would be a piecewise repair on a scale that large, of course). But the longer end of that estimate rests firmly at "a few years",
not "a few decades" (though most of the data I'm looking at is for the US, so other countries might suffer for longer or shorter periods depending on their own personal factors, obviously).