GRBs do Last only very short … 2 to 30 seconds … of a GRB hits a planet only a part of it will be toasted … the damage would be devastating for sure … but an advanced civilization would probably be able to recover (leaving the planet, or having well protected outposts) …

Which means a GRB could wipe out a civilization but it depends on its stage of development … it’s a matter of timing, which is reducing the probability of such an event dramatically and cannot explain the Fermi Paradoxon.

I would expect that Earth as a planet isn’t Especially interesting for potential aliens … all known invasion scenarios are about resources and empire building. Resources are endless in space, invading an average planet is far too costly, and empire building is also costly if the planet is still underdeveloped from the perspective of an advanced civilization.

Which means if there are aliens, we will meet them if the time has come …