This boi is the best at underwater metal(ore)working: https://en.wikipedia.org/wiki/Scaly-foot_snail
I’m surprised people keep bringing up hydrothermal vents for heat (not very significant to any metal but tin or lead, if good enough for boiling) but aren’t bringing up sulfuric acid for leaching, at least very often? ( https://en.wikipedia.org/wiki/Leaching_(metallurgy) ) Acid/toxin management and various sulfur compounds are part of life around a vent, and it would presumably already be pressurized … definitely other challenges to working with solutions underwater, but having salt + sulfuric acid + pressure + boiling water + chambers to keep your stuff in one place seems possible, and might at least change metal into a usable form. (Remembering precipitating silver from a solution now - results were pretty neat.)
If you did develop advanced-ish tech in an underwater, non-amphibious civilization, I’d guess that sulfur (and things like sulfuric acid) would have to be the key to do things we’re used to doing with fire, but can do with sulfuric acid and other sulfur compounds. (And vents being one of the richer sources of ores on the seafloor.) And the methods wouldn’t be very accessible to creatures that didn’t evolve along the vent, due to heat, toxicity from both vents and leaching methods, and pressure.
Tech tree might be a little too divergent from the fire-based one to make it easy to fit into the higher priority tech path, but hydrometallurgy is perhaps a better place to start than pyrometallurgy for underwater civs for anyone who wants underwater civs badly enough to program or mod something.