@john-ellenberger ,
In general, Notepad++ does update the time stamp when it writes a file… I have no problems with timestamps not being right when Notepad++ writes a file no matter where it’s written. This is likely because it’s not really Notepad++ that handles timestamps, but the OS interacting with the filesystem.
That said, Microsoft applies magic to lots of their tools, and Sharepoint is probably no exception.
Unfortunately, without access to a Sharepoint that I have write permission on (and without being able to figure out how to map a sharepoint location to Windows Explorer), I cannot replicate your problem.
Given that every MS search location for “map sharepoint drive” says something to the effect of “Mapping a network drive uses WebDav, an older technology which is slower and less reliable than syncing SharePoint files with the new OneDrive sync client. …”, I think MS is moving away from mapped sharepoint drives. If you have the option of accessing your sharepoint through OneDrive instead, that might be more reliable (and in OneDrive, if you tell it to “always keep this file on my computer”, then Notepad++ should have no problem writing to it and keeping the timestamp up to date… at least, I have never had a file saved from Notepad++ to my OneDriveForBusiness location not save the timestamp correctly).
Sorry I couldn’t give you a nice easy solution.
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edit: rephrased first paragraph, because certain readings made it look like I was contradicting myself