How to Disable FLAG_SECURE without root? I just realised the only way to bypass screenshot security on certain apps is to disable this FLAG_SECURE, which as I see can be done using Xposed module. 

But I don't want to root my phone. Is there any way to disable FLAG_SECURE and bypass screenshot security without root.
You might want to give Virtual Xposed a spin. 

It is an application that acts as a sort of "host" for other user apps you can install inside it. It then has full control over the process of the inner app, and can apply the functionality of some Xposed apps without requiring an unlocked bootloader or Root. 

However, it can only work for Xposed modules that don't modify the system. If your mentioned module tries to do that, VX won't be any good.