Thus, searching for “iPhone 6 9.3.6 untethered jailbreak” is a — the combination does not exist in Apple’s firmware catalog.

Historically, the "Home Depot" tool for iOS 9.3.6 was released as a tethered solution. However, the community has since retrofitted this mechanism to function as a semi-untethered solution (similar to the Odyssey/Guardian tool) or, in rare cases, utilized specific bootrom exploits for the iPhone 4 (though iOS 9.3.6 does not run on the iPhone 4).

p0laris is a semi-untethered jailbreak for 32-bit devices running iOS 9.3. 5 and 9.3. 6. The Apple Wiki Kok3shi9 - The Apple Wiki