[X6S1x6Okd1st]

I guess it depends on the algorithm they chose, HChaCha20 is the symmetric encryption algorithm for libsodium.js which is quantum resistant.

https://doc.libsodium.org/secret-key_cryptography/secretstre...

https://crypto.stackexchange.com/questions/79518/is-xchacha2...

[jmprspret]

Most if not all symmetric encryption is quantum resistant though (with a large enough key). Quantum computing only causes problems for asymmetric algorithms that involve factorisation iirc