Yes, though since it’s closed source, contains other proprietary libraries and probably was never properly audited (by a 3rd party) it’s possible (even likely, considering it’s Meta we’re talking about) that they keep a copy of the private key(s) and the messages, so that they’re able to decrypt them, and so still be able to gather the content, in addition to everything else, while they can publicly claim it’s all Signal’s protocol so everything’s “E2E”. And yes, the app also gathers a lot of other data (actual and metadata) besides the content of the messages (which Meta can’t supposedly see since it’s E2E, but I never trust anything from Meta). A Meta app (or Google, or MS, for that matter) should generate the same sort of privacy outrages and media/politics attention like TikTok does, but somehow they don’t. “Same shit, different country” was never so fitting.

Here’s a very good messenger comparison: https://www.messenger-matrix.de/messenger-matrix-en.html