context: Instagram will stop supporting E2EE chats starting May 8th, according to a new notice on its help pages.
Meta hasn’t clearly explained why encrypted chats are being removed or what happens to existing conversations afterward, raising new concerns about privacy, data collection, and surveillance on the platform.
Source: https://proton.me/blog/instagram-end-to-end-encryption
I don't use instagram but the fact that they are announcing they are removing the E2E encryption actually lends weight to the idea that it actually does provide some level of privacy. If it didn't, they wouldn't remove it.