I'd say 10 years is a good lifespan, maybe 15 if you're lucky.
Hmm, this Avera 40" 4K UHD TV, my first one I believe, around 2 years old by now, maybe a few months beyond, just had a strange grey vertical line in the Windows 10 desktop.
Moving around windows, and the line was still there. So I turned the screen on and off, and on the logo screen when it powers on, yep, you guessed it, grey line right where it was.
So I moved my stuff away from the front of the screen a little bit, and moved the screen a bit more forward onto the desk. Grey line went away. WHEW!
I hope that this isn't portending banding and bad "lines" to come.
The line was roughly above where the back of the desk is, in the back where the cubby is, where the PC is below, and heat from the PC (DC and mining) probably raises up in a column around there too.
My other one, I rebooted, and the HDMI was flashing alternative frames with blotches of static on it, at 4K60. I turned the TV off and back on again, and it went away. Weirdness. I had previously thought that was due to a GPU that had overheated, but this was a new GPU, and it behaved the same way. So now, I don't believe that that RX 470 that I recently gave away for the price of shipping, was bad at all. Or maybe all RX 470 cards have this defect from time to time with this TV model?