Looks like they happen on average every few thousand years. We really should be looking at how we recover from such an event, and whether we can do things in the design of power grids to minimize damage.
If there were humans living on the Moon or Mars these seem like they could be even more fatal unless they were living underground.
Given how profoundly useful and powerful electronics are, perhaps events like this are why electricity and electronics are not used at large scale by organic life. Have you ever wondered why humans and other life forms are so unaffected by EM that we can subject ourselves to things like MRI scans without even noticeable effects? Maybe there has been selection against anything that is vulnerable to EM because every few thousand years anything else is culled.
That’s why humans are ok with spending some time in an MRI, while microprocessors wouldn’t be.
For all we know the Sun is actually quite friendly to this. Most stars might behave this way more often. If that's true then intelligent life able to harness electricity and all it entails would be very rare. If our Sun did this every, say, 25 years there would never be an industrial/technological civilization here... or at least not a sophisticated one able to build things like spacecraft.
In any case this is something we should be studying a lot more than we are. It is a far more tangible and realistic existential threat than very hypothetical AI apocalypse scenarios.
My memory is not very clear, but I remember it was around 48 hrs.