Sell the locked device on eBay as "iCloud locked / parts only." Let a refurbisher with a Purple Tool deal with it. iOS 9.3.6 marks the end of an era. It is the last operating system where the user had any real control over the activation process. Starting with iOS 10, Apple introduced hardware-based cryptographic checks that make permanent bypasses virtually impossible without Apple’s private keys.
Updating via iTunes or OTA does not remove the Activation Lock. Furthermore, if you attempt to force-update iOS 9.3.6 to iOS 10 or 12 (using unsigned builds), you will likely encounter error 3194 (invalid firmware). And if you succeed? The lock is still there, except now it's on a slower operating system. ios 9.3.6 activation lock bypass
If you have purchased a used iPhone 4s or an old iPad from a garage sale, only to be greeted by a gray screen asking for the Apple ID and password of a previous owner, you have met the Activation Lock. For modern devices (iOS 11+), the solution is simple: contact the owner. For iOS 9.3.6? The answer is far more complicated. Sell the locked device on eBay as "iCloud