Port knocking was somewhat silly when it was introduced ~20 years ago --- at most, on a reasonably designed network, it was saving you from your own misconfigurations, but at least in 2005 it was reasonable to imagine a highly diverse network of machines that people logged into using multiple protocols, where those misconfigurations were likely.

In 2020, it's gone past "silly" and is now a design smell, in the same way that actually relying on fail2ban would be. Whatever port knocking is doing to help you is a a description of something you're doing wrong with your architecture.

We're not even comfortable with long-lived keys anymore; modern networks are built with short-lived certificates issued off 2FA from an IdP. We have good VPNs right now for the other weird cases. Our networks default to all-ports all-hosts closed. Arguably, port knocking is literally setting your security back, by making it harder for automated tooling to scream bloody murder if you've managed to expose a dev instance unexpectedly to the Internet.

Don't bother. If you've got a single system you're managing outside of a cloud provider with its own decent network firewall, just set up WireGuard and filter everything but that. If it helps, think of WireGuard as the evolution of SPA port knocking.