I think there are some things that we can be sure of anyway.
For example, no kind of “cracking”, quantum or otherwise, can decrypt a message without knowledge of the encryption key, provided that a big enough key is used.
I think this can be understood in the following way. Let’s say the two of us are about to exchange some messages, knowing that others can snoop on our messages in transit. Before starting our communication we meet physically and exchange encryption keys. We have 1000 different keys, and each key is long enough to cover a whole message. The encryption scheme could be simply that the key tells us how each byte in the message should be scrambled (e.g. an XOR cipher), but each byte in the key is only used to decipher one byte of the message, no part of the key is ever reused. Apparently this is called a One-time pad.
If we met physically and exchanged 1000 such keys, we can later send 1000 encrypted messages without ever reusing any of the keys. We could prefix each message with a clear-text number telling the receiver which key to use.
If we did it like that, it would not be possible to “crack” our encryption no matter how cool and powerful quantum computers the snooping people have access to.
The point is that cracking encryption using computing power (quantum or not) is about exploiting the weakness that comes from reusing the same key many times to encrypt a lot of data. If encryption keys are never reused, computing power does not help.
Anyway this is what I think as an amateur cryptographer, please correct me if I’m wrong!