I'm not sure if this is 100% serious but if it is, how could the FBI having a backdoor into every messaging app fit in with the relative ineffectiveness of the FBI?[0] If they truly did have the ability to spy on any messaging app without issue then you would expect them to have far more success than they actually do. For comparison, a quick Google search says China has a 99.9% conviction rate. Remember security and intelligence agencies also want people to think they are some omnipotent and omniscient entity that you cannot escape from, even though we know this is far from true[1][2].

[0]: https://time.com/magazine/us/5264136/may-14th-2018-vol-191-n...

[1]: https://www.nytimes.com/2017/05/20/world/asia/china-cia-spie...

[2]: https://www.nytimes.com/2021/10/05/us/politics/cia-informant...