I gave you a citation, that is about GRBs and interaction with the atmosphere. That's where 100 kJ/m^2 comes from. First page, even, it's in the abstract.
Radiation absorbed dose is measured in Grays, which is Joules/kg, and 8-30 J/kg is the lethal range I gave you, easy to find with trivial search but also so well known you shouldn't need to be told about it if you're serious about rad hazards.
You get from J/kg to J by accounting for mass, and from kJ/m^2 to J by accounting for cross sectional area. Hence 25 kJ actual, and 1 kJ lethal limit.
You can look up radiation mean-free-path shielding constants if you want, but I'm not walking you through what is foundation-level knowledge in this domain. Me, I got that knowledge by having an interest in atomic rockets and fusors back at university, it's not hard to find.
If you can't apply the inverse square law to get Martian sunglight relative to Earth's, or if you don't know about its missing ozone layer or missing magnetosphere, you have no business even thinking about a Mars colony.
At this point, why expect an AI based answer to miss citations when they've got a big friendly button saying "search" right there in the web UI?
No.
A GRB strong enough to reduce Earth's ozone layer by half, would be about 100 kJ/m^2:
https://ntrs.nasa.gov/api/citations/20050179464/downloads/20...
On Mars, where there's no ozone layer in the first place, and the atmosphere is much thinner, and there's no magnetosphere, IIRC just over half the radiation from a GRB reaches the ground.
Given a human cross-sectional area from above is about 0.25 m^2, that means that a human outside during such an event would get 25 kJ almost entirely absorbed by their body.
A lethal dose for a 100 kg human is about 1 kJ absorbed. And when I say "lethal", 1 kJ absorbed is 99%+ lethal within 2-14 days, even with immediate treatment, and the victim suffers rapid incapacitation due to CNS failure.
You'd need to bury everyone under, IIRC, 2-3 meters of regolith to protect against that. You'd also need your crops underground for the same reason. If you're going to all the trouble to have a farm functioning under several meters of soil, you can also do the same things needed for that, on Earth, far more cheaply.
Furthermore, the nitrogen dioxide levels expected in such an event, would reduce Earth surface sunlight levels by 10-60%. Mars, just by being further from the Sun, gets a reduction of 48-64% (varies over the Martian year) relative to Earth — even when there's no planet-spanning dust storms, which it also gets.