bookreader Out of date devices don't just suddenly turn into unusable messes of security holes. They can still be quite secure and usable for a long time.
Having said that, of course vulnerabilities will be discovered over time that may apply to them. But the question then is this.... does it matter?
If a vulnerability is found in a supported device, it can be reported for a bounty and then patched. But if a hole is found in an obsolete device, maybe the only way to take advantage of the hole is to use it to steal things from people... or use it to recruit a node in an ad-fraud network or a DDoS botnet.
So an unsupported device and a supported device might both have zero publicly known vulnerabilities, but the unsupported device might be 10X or 100X more vulnerable.
bookreader If the device doesn't have access to any security sensitive data, then it will be more just an inconvenience if its compromised than an actual loss. If the device isn't used for anything that makes it possible for an exploit to be used on it, then it won't become compromised.
If an old 3a has Wi-Fi and cellular data and Bluetooth turned off, and is used as an alarm clock, that's pretty safe, or if it is used as a camera and pictures are extracted via a USB drive. The more time an out-of-date device spends on more/faster networks, the less safe the situation may be.