you took all the right actions, but salt water is a really tough nut, followed closely by pool water.
only thing i would have done differently is to do a full day soak in 99% IPA, with a couple of very gentle scrub sessions with a very soft toothbrush, then swapping the IPA with fresh and a couple more very gentle scrubs. finally a rinse with new IPA and letting it air dry for at least a couple of day.
because there are other parts involved. because you can't see anything on the screen could mean that the display is kaput.
if you happen to have a usb volt/amp meter you can see if the charging circuitry and battery are drawing power.
ideally though, i'd put the motherboard into a different, known, good, working phone (of the same model) and see what happens. that's not an easy option if you don't have extra phones lying around. but if you do have life, you can at least do a backup, then if you really want to recover your phone, you can work backwards from there to troubleshoot which items in your phone are dead and need replacing, and which ones are still good.