I obtained a broken P4 that had been sitting at the bottom of the ocean for some time. It's obviously never ever going to fly again but I managed to pry out the internal SD card from the flight data recorder and extracted some large flight logs in the form "FLYXXX.DAT". I'm wondering if these files can be read/converted somehow without the actual P4 drone? I tried some tools that supposedly work for P3 models but couldn't find one that worked for me?

Adam, you cannot access to the DAT.
If it needs to be analyzed, customers need to export the flight data and upload to DJI, our engineers will help you all handle it.
Since the P4 is watered, then it will not function well.