Maybe for an extended path it could try _getfinalpathname without the prefix. If it isn't a valid path or the result isn't the same as _getfinalpathname including the prefix, then skip calling _ext_to_normal. For example:

    def resolve(self, path):
        s = str(path)
        if not s:
            return os.getcwd()
        if _getfinalpathname is not None:
            prefix, t = self._split_extended_path(s)
            s = _getfinalpathname(s)
            if prefix:
                try:
                    if _getfinalpathname(t) != s:
                        return s
                except FileNotFoundError:
                    return s
            return self._ext_to_normal(s)        
        # Means fallback on absolute
        return None

The 'foo.' path in this issue would keep the prefix:

    >>> Path('//?/C:/foo.').resolve()
    WindowsPath('//?/C:/foo.')
    >>> Path('//?/UNC/server/C$/foo.').resolve()
    WindowsPath('//?/UNC/server/C$/foo.')

But regular paths would remove the prefix:

    >>> Path('//?/C:/bar').resolve()
    WindowsPath('C:/bar')
    >>> Path('//?/UNC/server/C$/bar').resolve() 
    WindowsPath('//server/C$/bar')

On a related note, _split_extended_path only looks for uppercase "UNC", which makes the above resolve method fail:

    >>> Path('//?/unc/server/C$/bar').resolve()
    WindowsPath('//?/UNC/server/C$/bar')