I was able to do this with my TCL/Roku TV a few months back. My curiosity got the best of me with the announcement of their latest OS, so I upgraded to see what the new features were like. Now I am stuck in the ecosystem, as the downgrade feature is completely disabled (even from a USB stick, with no internet connection, after a factory reset). Luckily, I use a Pihole as my DNS on my router, but still. Super annoying.