I have files that get rename after they're processed to something like this: FileOne_202007241237.txt
The files can have any number of different extensions.
I need to move and rename the files, without the dateTime part for reuse with a different process.
So FileOne_20200724123.txt needs to become FileOne.txt

I need to do this en masse using a regex for the date time part so that I can rename and move all at the same time.

Any thoughts?

This "remembers" only the parts before the underscore and the extension, then puts them back together, leaving out the underscore and anything after it until the extension:

{REGEX(Replace|FileOne_20200724123.txt|(.*)_.*(\..*)|$1$2)}

Assumes only one underscore.