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I know a repeat of the 1859 Carrington Event (coronal mass ejection) would pose a severe risk to power grids and telecommunication networks but wouldn't pose an immediate threat to life.
If a large solar flare can release 10e32 ergs of energy, is there an energy level where a solar flare or CME would pose an immediate threat to any life on the Earth that doesn't live below sea level.
Abrevaya et al. (2020) in "The UV surface habitability of Proxima b: first experiments revealing probable life survival to stellar flares" (abstract, PDF) say:
"Our results show the impact that a typical flare and a superflare would have on life: when microorganisms receive very high fluences of UVC, such as those expected to reach the surface of Proxima b after a typical flare or a superflare, a fraction of the population is able to survive. Our study suggests that life could cope with highly UV irradiated environments in exoplanets under conditions that cannot be found on Earth. "
That suggests that total-extinction conditions aren't found on Earth, either. The paper has a lot more detail of their assumptions and modeling, but that's my quick takeaway from the abstract.
I would say, that with our current atmosphere and magnetic field there's not a "direct" threat to life as they shield the Earth.
The atmosphere is opaque to X-ray radiation that can come from outside. It seems that much of that opacity comes from water vapor, and the amount of that in the atmosphere changes depending on different factors. X-ray radiation has also effects on the ionosphere and can change its size, which affects communications but I don't know whether life is affected for that.
Earth's magnetic field is disturbed by a CME and that has also various effects like inducing currents that, as you said, pose a risk to power grids and telecommunications. However there's another effect that's also associated with CMEs and solar flares: Solar Energetic Particles, these types of events are, I believe, the one that could have a more direct effect to life. If they are happening together with the disturbance of the magnetic field produced by a CME, then our shield is weakened. The maximum flux of the chain reaction they produced when they reach Earth happens at 18km above the sea level, and at the altitude of a commercial flight is ~300 times more than at sea level. However, only seems to pose a "risk" to frequent flyers (crew and passengers) as the cumulative effects could produce cancer. I've extracted these numbers from the Extreme Space Weather report by the Royal Academic of Engineering and references therein.
