sadly, you’re wrong in this instance.

The mission made up of Ms. Patten and nine experts – which was not investigative in nature –… (emphasis in original news brief).

According to the actual report:

The present report is submitted to the United Nations Secretary-General pursuant to the mandate of the Special Representative of the Secretary-General on Sexual Violence in Conflict (SRSG-SVC), outlined by the Security Council in resolutions 1888 (2009), 1960 (2010), 2106 (2013), 2331 (2016), and 2467 (2019). This report contains the findings of the mission of Special Representative, Ms. Pramila Patten to Israel

(emphasis added)

So, she wasn’t a no-name 3rd party, but wasn’t an investigative envoy.