https://x.com/runasand/status/2017659019251343763?s=20
The FBI was able to access Washington Post reporter Hannah Natanson's Signal messages because she used Signal on her work laptop. The laptop accepted Touch ID for authentication, meaning the agents were allowed to require her to unlock it.
It's interesting in the case of social media companies. Technically the data held is the companies data (Google, Meta, etc.) however courts have ruled that a person still has an expectation of privacy and therefore police need a warrant.