The catastrophic eruption of Santorini is certainly not imaginary. It did erupt explosively and catastrophically as the geology clearly demonstrates. Its role in the destruction of the Mediterranean civilizations of the period is a different question. There is abundant evidence that the Sea People came from Northern Europe in a mass migration after yet to be fully described catastrophes drowned the coastal regions and destroyed the agriculture in the region. It is not uncommon for migrations and invasions to occur in the wake of major ctastrophes. The massive destruction in the wake of Santorini and/ore the sequence of major earthquakess occuring in the Eastern Mediterranean about this time give good reson to suspect the Sea People were exploiting an opportunity made available by the catastrophe.s.
There’s no evidence that there was a mid-2nd M “supereruption”; the eruption that put a few inches to a few feet of crud over Akrotiri is attested from one surviving ancient source, and dates to about 200 BC. There’s literally nothing to any of the late-19th c claim (that is when it originated) that is supported by geology. There’s a lot of CLAIMS that there is support, but none of them make sense. There’s a tiny (mm’s thick) layer of ash found in one end of Crete; there’s zero evidence of any tsunami; the caldera is prehistoric by 10s of 1000s of years; and it would be reasonable to expect the tsunami to have headed for the Greek mainland, given the way the crater now opens to the sea (again, that event was prehistoric).
There’s no evidence that the Sea People existed as they’re described today, and zero evidence of any homeland, except for assignments of modern placenames that sort of match the list in one Egyptian account. Given that there was no supereruption, that the conventional pseudochronology places the Sea People 300 to 400 years *after* the supereruption (which , though fictional, is dated from 1628 BC up to and through 1500 BC; Sea People dated some time after 1200 BC), even the math doesn’t work.
The (apparently) most recent Linear B texts that survive have Latin loanwords, which can’t be explained except by the obvious errors in dating in the conventional pseudochronology — Linear B remained in use, parallel with classical Greek writing, until sometime after the Romans arrived in Greece.