If you were to develop this tool, ideally it would have to work only on the desktop. I do not think that the vast majority of smartphones have performance for this without compromising performance.
In social media it is more common, but given the movement of facebook and others to fight fakes, the environment in messengers is practically uncontrolled. I believe there will be a migration from the type of falsehoods to messaging applications because they cannot be censored.
I am not the type to preach or believe in the need for corporate and government surveillance on messengers. This is absurd to me. But if there are tools that make it possible to identify a deep fake in a way that guarantees privacy above all, for me it’s fine.