sure, you can play lawyerball and say its possible.
yes, AFTER 40 THOUSAND YEARS, we humans have figured a lot of this stuff out in an easy environment. Sure, we can take the knowledge we have gained over the last 40k years, and do some stuff under water, because we have already figured it out.
i also hate your type of person. your the type of person that says: give me evidence, you are wrong until you give me evidence. but you provide none of your own.
But we've already had one such event-- the development of human intelligence. So if the random emergence of sentience from undirected physical processes is your bar for impossible, I'd say you need a new bar.
Regarding human technology, 40 thousand years is not a lot of time in the grand scheme of things. But even having said that, none of the claims I make rest on having human tech: the electric eel is not a human invention, nor are lorenzini organs. Use of a lava flow for heat is natural to many aquatic ecosystems, and requires no more intelligence than the ability to win at "hotter or colder". Many aquatic life forms already make use of simple hydraulic effects to move along the sea floor, anchor themselves into tidepools, or hunt prey. The preponderance of evidence we have for life on Earth suggests that that these skills will develop over time. Proposing that there is some reason that advancement inevitably stops under the sea is a bold and surprising claim, and yes-- requires evidence.
Regarding hating my type of person, that's on you. I think your position is narrow-minded and in error, but I'm pretty sure you're not Hitler.
Electricity is far from impossible either to develop or use underwater, and in fact nature has already done so in the form of the electric eel. More to the point, many aquatic species have specially developed sense organs for electricity, increasing the odds of it being developed for communication.
Similarly, although it doesn't look much like your childhood campfire underwater lava flows can be stable and useful sources of heat great enough for refining ores and similar. Further shaping using hydraulic pressure (equivalent to waterjet cutting or forming) would hardly be unimaginable.
And please feel free to say your mean things-- it certainly can't damage my view of the evidence you've put forth so far.