https://www.nccgroup.com/media/fzwdxklh/_ncc_group_whatsapp_e001000m_report_2021-10-27_v12.pdf
https://eprint.iacr.org/2023/843.pdf
Also, their e2ee is built on the signal protocol. Now, their server code and client code are not open source, so they could have left all types of doors open for their benefit. Also, the Metadata is not encrypted at all, something they actually brag about for some reason.
And just to be clear, I am a genuine 'everything-meta-hater" (and Google, MicroShit, Crapple, Crapsung, etc.), but spreading misinformation doesn't help preaching about privacy and security.