This powershell script was written to run on Windows 10 using GPX data saved using various Garmin tools.
This Git repository has a script that will allow someone who wishes to rename all their .gpx files according to the first timestamp found in the file. Reason: Various tools name these files differently. My requirements are to have all these gpx files saved in gpx data time stamp sequence. (I'm only interested in what the first date of the file is so I know the time sequence of the recorded data.) I have also numbered the files in the order they were processed giving each file a unique name. Reason, Some gpx files may have the same first time stamp.
I have accumulated thousands of gpx files over the years using various "Garmin" devices that are saved on my Windows OS.
Recommendation; Search all your data on your HDD's for .gpx files and copy them to a central location. Once that is done I recommend doing a DeDup on the data using a byte by byte comparison. I use a tool called "AllDup" http://www.alldup.de/en_download_alldup.php - (byte - byte check... keep oldest file).
So what is a GPX file. I recommend reading the following from here: https://www.topografix.com/gpx_for_users.asp