A practical quantum computer would be capable of breaking almost all modern public key cryptography.
There's an entire field of research dedicated to figuring out what we'll replace those algorithms with if quantum computing does become practical on a significant scale: https://en.wikipedia.org/wiki/Post-quantum_cryptography
Most side-channel attacks have mainly been a threat to the implementation of cryptographic systems and algorithms. Now
Specter and Meltdown have brought that concern to all systems.
The gist of the parent post is, create complex systems and these things will bite.
There's an entire field of research dedicated to figuring out what we'll replace those algorithms with if quantum computing does become practical on a significant scale: https://en.wikipedia.org/wiki/Post-quantum_cryptography