What is the bridge between Facebook, google, twitter, ig etc?
The bridge Q mentions cannot simply be a measure of a nodes centrality in a graph. It has to be juicier, but this is a good start. Not a centrality measure, but a system of central command and control.
So what connects the platforms?
Alphabet Agencies.
They have built a sociological controller to manipulate public opinion, and the big social media sites do the information gathering and manipulations.
A system of control depends on gathering legible signals and organizing those signals in a space that the controller can navigate. This is exactly what Bill Binney solved when he invented metadata analysis.
A centrality measure could be used in this context to find efficient, legible representations of the data from social media sites.
For example, in a graph of competing beliefs or ideas (a mimeograph) , a bridge centrality measure would likely be able to identify a good "compromise" position.
In a network of users connected by shared political beliefs it would be able to detect people who read both sides, or are open to persuasion.