Apple TV 4K "Update was not successful"

Since October, I have had playback issues across multiple apps on my Apple TV 4K. Assuming something was not updated, I went to make sure the software was up to date as it should have been automatically updating. It was not updated to the current tvOS, and when I went to update it manually, it stops suddenly and returns the message "Update was not successful. Please try again later."

Since that time, I have tried multiple solutions on my own, with the help of Apple Support, and searching various online forums for solutions. These include, but are not limited to:

• Restarting (using 'Settings' and via the remote)
• Resetting (both 'Reset and Update' and plain 'Reset')
• Power cycling, leaving the Apple TV off for 30 seconds, 2 minutes, 5 minutes, 30 minutes, or 2-3 hours.
• Power cycling + restarting + attempting update
• Power cycling + 'Reset' + attempting update (both with and without setting up the Apple TV as it was before)
• Power cycling + 'Reset and Update'
• Taking it to an Apple Authorized Repair Center (though not an Apple Store, they haven't had an appointment available since I've been trying before Thanksgiving)

None of these options have been successful. Each time an update or 'Reset & Update' is attempted, it returns the "Update was not successful" message either in the middle of downloading the update, immediately after completing the update download (according to the status bar) or in the middle of "Step 1 of 2: Preparing the Update."

Current tvOS is 14.0. When I started this process I was trying to update to 14.2, though now the current version is 14.3.

The Apple TV 4K was originally purchased in May of 2018. I have not had any noteworthy issues with it until this, where now some apps are virtually inoperable due to inability to sign-in or severe playback issues. Virtually no apps are free from playback issues at this point. Occasionally there are even display errors/artifacts (see picture).

It is incredibly frustrating that a device stopped functioning on its own, through no fault of my own, without any discernible hardware causes, and no one at Apple is able or willing to solve the issue for me.