Wondering how to verify devices are still not compromised after reset?

Question

So I am wondering how I can possibly verify different devices that I purchase. Like when you want to verify a file has not been changed you can verify the checksums. So for example, if I buy a new Android device, a new washer, IoT devices for the most part. Is there a way to check something so that in 2 months down the road and I want to do a factory reset and make sure that no unauthorized changes have been made that have stayed over to the hardware/software? I am guessing this would be quite difficult? And I'm also thinking this would not be possible with Android due to the system retaining software updates probably like most things. So if anyone knows of a good way to do this, I would like to hear it. I know you can reflash everything but with different OS, IoT, and such it would probably be very time consuming process to figure out how to reflash each device. Is there a way to snapshot these devices after you buy them.?