It's fiercely debated but as time goes on it seems like it is at least partially true. I'm guessing that some effects of radiation really do map better to LNT whereas others map better to radiation hormesis; why and when is a mystery, I think. Maybe some folks more vested in this topic have an idea.

The most fascinating example of hormesis I can think of is that after the atomic bombing of Hiroshima, some people who would've received a relatively small dose of radiation seemed to have a slightly lower cancer risk than people who wouldn't have received any additional radiation.

https://pmc.ncbi.nlm.nih.gov/articles/PMC6937943/

I'm sure there is plenty of debate about these studies and their methodology, but I have some suspicions. There seems to have been a lot of handwaving and intentional omission to explain away or ignore why LNT didn't seem to match reality. Radiation hormesis may be an illusion itself, but as it stands it appears LNT is unable to explain experimental evidence sufficiently. We're clearly missing something, and there is a lot of potential conflict of interest, especially given the obvious incentives for the energy sector...

But also, I just read Wikipedia and watch YouTube causally, so hell if I know.