Sony TVS suffer from dying eMMCs, and there's very little info or flash dumps available, plus they use heavy security so they won't boot if anything strange is found.
Finally they store the keys in the rpmb partition which nobody can access.
Happened to me 2 years ago, it started with those random bootloops and serious slowdowns.
Started reading possible issues, found that, bought a new chip and copied the flash contents.
The flash was partially damaged, also eMMC health was 0%, I was able to only extract 75% of the system partition, but it worked anyways.
Lost the keys in the rpmb so no more Netflix/Chromecast, bought a Chromecast with Google TV and that was it.
It's absolutely stupid that a $900 TV dies after 5 years because of the flash wearing out.
Now I only use it like a dumb TV, no updates, no Internet, like it should be, let the Chromecast take the hard job, if it dies just replace it, $50 and done!