ncmm.exe: which program is it?

ncmm.exe is a normal part of ncmm when it sits in the program's install folder and carries the publisher's digital signature. A file with the same name in another folder can be something else: check its signature and hash.

In the program's install folder, which the installer chooses; winget puts portable programs under %LOCALAPPDATA%\Microsoft\WinGet\Packages.

Uninstall ncmm through Settings → Apps or with winget; the uninstaller removes ncmm.exe with it. Deleting the file alone leaves the rest of the program behind.