LED strips quit working
Think about it.  If the LEDs were failing, they would fail individually one at a time, not the entire strip at once.  (strips typically have many LEDs, but in groups of 3-6, so if an LED was failing, it couldn't take out more than 6 at a time).
What's failing is the power supplies
And this is typical of the failure mode of cheapie LEDs.   The LED emitters are solid as a rock and will outlive us all. But they are bundled with a power supply that fell off a truck in Shenzhen.  This is especially likely with the mail order/China/eBay/Amazon Marketplace jobs.  Amazon Marketplace is third party sellers, and their junk is intermixed with real &quot;sold by Amazon.com&quot; listings. It's very hard to tell the difference.
Fortunately, these power supplies are commodity items and can be easily replaced. You simply need to look closely at its specs and find a higher quality one.  Meanwell is a popular balance between price and quality, and is widely used on better lights.