This is a simple script for backing up your single player save files
The script creates a new folder named as today's date and time, e.g. 2021-11-10_1906 for 7:06 PM on November 10th, 2021. Then it copies all the files from your Diablo II save folder into a folder named LoD in the dated folder, and all the files from your Diablo II Resurrected save folder into a folder named D2R in the dated folder.
To use, edit the save paths stored in the DIABLO_II, RESURRECTED, and BACKUP_FOLDER variables to match the full paths to the directories on your computer. Then simply double click on backup.bat to execute the script and backup your save files.
You can put the script anywhere you like, and even create a shortcut for it (e.g. on your Desktop) if you want to.