I can certainly help explain what to look for when examining — especially those that have been patched from earlier versions (like 1.10–1.13).
Paste %USERPROFILE%\Saved Games\Diablo II into your File Explorer address bar.
To bring a character forward, you simply copy the .d2s file from the old "save" directory to the new modern path: C:\Users\[Username]\Saved Games\Diablo II Resurrected .