There was some good reporting on this issue in the Twitter Files. For example, Jim Baker, the general counsel at Twitter, used to work for the FBI. Musk fired Baker for his role in suppressing the Hunter Biden laptop story.

https://jonathanturley.org/2022/12/04/six-degrees-from-james...

Found the source[1]. It includes names and LinkedIn profiles, so ought to be verifiable.

[1] https://www.mintpressnews.com/twitter-hiring-alarming-number...

That covers twitter, now what about every other social media network. The claim was that this was happening for all of them.

Oh sorry, you're right. Here's an article[1] about Facebook, from the same outlet. With some cursory searching I couldn't find anything about other social networks hiring former three letter agency employees.

[1] https://www.mintpressnews.com/meet-ex-cia-agents-deciding-fa...

The same outlet also covered Google: https://www.mintpressnews.com/national-security-search-engin...

Here's another good source about Google's revolving door with government during the Obama administration: https://www.techtransparencyproject.org/articles/googles-rev...