Depends on the conditions, I’d say. If you have an area that has low oxygen and high saline concentration, one could potentially preserve large parts of the carcass. A big challenge though is the substances brought by the carcass itself, like enzymes and bacteria that are not directly exposed to the oxygen-deficient saline-abundant water, which can thrive and remain active for a long period of time. However, if this carcass sinks to incredible depths, where the pressure is really high, temperature is a constant 4 degrees, very low concentration of scavengers or thriving organisms, and potentially sinks a bit into the sediment for a long time, you’ll essentially get pickle juice fossil fuel.

They only recently made it mandatory for three visa types, but since introduced in October 2016, it’s always been an optional field when applying for an ESTA.

Edit:
Not that not providing your social media handle will benefit you, of course.

Depends on the level of technology you’re willing to go to:

Smart phones today you’re probably all out of luck, whether it’s Google’s Android, Huawei’s HarmonyOS, or Apple’s iOS. Same with any desktop PC.
Dumb phones without internet connectivity, like the Mudita Pure, can get you pretty far, but as you’re making calls and sending texts through your telecall provider, your provider might use that data for training purposes still.

For other technological devices, like fitness trackers, TVs, cars, fridges, or any IoT device really, that somehow either connects to internet or syncs to a device with such capability (your phone) in order to phone home, you’re likely out of luck.
Dumb devices, like mechanical timepieces, monitors, and “normal refridgerators” can get you pretty far, but remember that your purchases of these things, along with all the metadata of those purchases, might also be tracked and trained on.