The name "post quantum encryption" sounds super complicated, and to be fair the math behind it is beyond my understanding (and I won't even claim I would have enough time in my life time to study it and assume I can formally prove all of it to be correct) yet switching is actually relatively trivial, namely your software, say a browser like Firefox or Chrome, and the server it communicates with, e.g lemmy.ml relying on e.g nginx or Apache, "just" have to have at least 1 matching encryption scheme, one way to exchange data that is post-quantum resistant. In practice that means configuration files on both sides that you, as a user, do not even know exist and that can be done through basic updates.
TL;DR: most users will switch to post-quantum encryption without even realizing, and then even if say the NSA were to buy a $1T quantum computer, even your $1K computer and the $10K server it communicates with would be able to handle it no problem, even a $30 Raspberry Pi computer will.