tl;dr

The FBI made a note that they've accessed the phone, shared by NYT etc, https://www.nytimes.com/live/2024/07/15/us/trump-shooting-in... , there isn't any other information.

https://www.fbi.gov/news/press-releases/update-on-the-fbi-in...

Details on whether this was before first unlock or not remain unclear. If the FBI is smart, they won't divulge that information.