Sysdiagnose log files are located on iPhone in Settings > Privacy & Security > Analytics & Improvements > Analytics Data. Sysdiagnose is a tool that collects information from the iPhone and saves it in a log file. You can use sysdiagnose to troubleshoot general iOS issues or report them to AppleCare. To generate a sysdiagnose log file, you need to press and hold both volume buttons and the side or top button for 1 to 1.5 seconds, then release them. You will see a screenshot and a message that says "Diagnostics are in flight".
Sysdiagnose can take up to 10 minutes to finish. After that, you can find the log file in the Analytics Data section of the Settings app. The log file name will start with "sysdiagnose_" and include the date and time of the generation, the device type, and the iOS version. For example,
"sysdiagnose_2024.01.06_17-14-34+0500_iPhone_OS_iPhone_19A344.tar.gz". References: Using Sysdiagnose to Troubleshoot iOS or iPadOS - Apple Device Support Tutorials | Apple Training, How to extract sysdiagnose logs for forensic purposes on iOS | Andrea Fortuna