Notepad++ Regex pattern issue (valid on online regex testers)

I have the below pattern:

".*\(.+)[rn]?(.*)"

Being applied against the following text:

"c:usersjdoeOneDriveFolder 1Folder 2File 1.pdf
File 1.pdf"
"c:usersjdoeOneDriveFolder 1Folder 2File 2.pdf
File 2.pdf"

Designed to return:

File1.pdf
File1.pdf
File2.pdf
File2.pdf

It does so as expected on https://regex101.com/ (https://regex101.com/r/51qy3T/1), on every flavor of Regex apart from .NET (no escaping of the "‘s, but with that removed also matches).

But put into the Replace window of Notepad++ and it says it is Find: Invalid Regular Expression at the bottom of the Replace window. Am I miss debugging that could explain to me why, given it seems to be valid in quite a number regex flavors, or does anyone know what I missing?