Definitely, but when we're running around sprinkling PQ algorithms all over the place, it's on top of the asymmetric bits, not replacing the "boring" stuff like your symmetrically encrypted backups. Shit certainly does happen, especially where key management is involved, but I'm not sure I agree that offering an encrypted backup feature is necessarily undoing the FS/PCS story.
edit: Well, let me argue with myself for a moment. I don't think offering an encrypted backup feature undoes the PQ story. But FS/PCS is weakened, sure, since we're talking about all types of shit happening, not just currently known (or strongly theorized) attacks.
What type of static key? If it's just a big symmetric key that isn't derived from an asymmetric handshake of some type then no, that's not our current understanding of the PQ threat model.
I don't think that's quite right. PQ attacks focus on the "trapdoor" functions in asymmetric cryptography, _not_ the symmetric encryption that happens after key negotiation. The current concern is that a future attacker could unwrap the symmetric key, not directly attack the symmetric encryption that is used for something like backups.
(Note: I didn't actually dig into the backup implementation, but my guess is that it's more of a KDF -> symmetric design, rather than the sorts of asymmetric negotiation you'd find in multi-party messaging.)
To be honest I sometimes get better signal from things like cucumbers than I do with technology. Tech has a real issue with biasing towards people who happen to have worked on a particular topic, and as we all know we get bounced to unfamiliar topics constantly.
edit: Well, let me argue with myself for a moment. I don't think offering an encrypted backup feature undoes the PQ story. But FS/PCS is weakened, sure, since we're talking about all types of shit happening, not just currently known (or strongly theorized) attacks.