Take the Nuclear Option and Turn Your Bravia Into a "Dumb TV"
First off, get an external Android TV device (Nvidia Shield, Mi Box S, etc.).
Second, create a dummy Google account for signing into your TV.
Next, fully update your Bravia until no more firmware updates are available, this will ensure you have the newest TV settings menus/features.
Now, factory reset your Bravia.
After factory reset, sign in with your new dummy Google account.
The biggest step, you can turn your Bravia with Android TV essentially into a dumb TV and use an Nvidia Shield or similar instead by using the built-in, hidden Pro Mode settings to disable most of the Android TV features. When your finished, your TV will just boot up to an input screen, the home screen won't have anything except inputs, but all the settings screens will still be available to configure and use all the nice processing features built into your Bravia TV (HDR, Motionflow, Digital Noise Reduction, etc.).
Sony's Official Pro Mode Instructions (for reference): https://pro-bravia.sony.net/guides/mode/
How-To Video, Demonstrating Pro Mode Usage: https://www.youtube.com/watch?v=o7R6D3ElCc8&t=52s
Final step, disconnect your Bravia from your network completely. With the 3rd party device being used for Android TV now, there's no need to connect your Bravia any more.
Why do all of this? As we know, Nvidia does a great job keeping their Shield devices up to date and provide the best Android TV experience there is. Notable runner up is the Mi Box S.
With vulnerabilities in mobile OS devices always being found, and with Sony's neglect with updating all of their Android devices, including Bravia TVs, that leaves one new approach vector as an avenue for not only your TV to get hacked, but your entire Google account and possibly your entire home network as well.
For example, my x850c has not had a security update since May 2019; others here haven't seen an update for their Bravia TVs for 1.5 years. Google has patched Android with security updates numerous times in the past 6 months that my x850c is now lacking. A 6 month window for providing security updates, if they even supply them at all is not acceptable in this day and age. For a TV that originally ran $2400 at launch to barely get security updates after the 1st year is unacceptable. I personally do not buy Bravias for the Android TV/Smart TV experience, but instead for the great picture quality, post-processing tech, etc.
By turning your Android TV into a dumb TV, you are securing your Bravia more and instead getting a much better, faster and stable and customizable Android TV experience with a 3rd party Android TV device.
Mi Box (Oreo): ~56 days (https://postimg.cc/4mFsdSFZ)
Shield TV 2017 (Pie): ~58 days (https://postimg.cc/1V31RGGf)
Both boxes are fairly stable lately without any noticeable slowdown. Both are loaded with many apps & games with adoptable storage and used regularly for video streaming and some gaming (Mi Box is mostly limited to 2D games and emulators). Mi Box used to have occasional wakeup issue due to losing pairing with remote. But with Wakelock fix, I am always able to wake it up now with casting from phone. Shield TV used to experience rare auto-reboot once every few weeks when adoptable storage is unmounted. This hasn't happened since the Android Pie update.
Please share your experience, preferably with screenshot.