In basic terms... this is a technical detail that isn't going to impact Kubernetes users (a mass majority of them). Those who are concerned with running their workloads in Kubernetes, anyway.
The part of Kubernetes that runs containers has had a shim for docker along with an interface for runtimes to use. It's called the Container Runtime Interface (CRI). The docker shim that worked alongside CRI is being deprecated and now all runtimes (including Docker) will need to use the CRI interface.
These days there are numerous container runtimes one can use. containerd and cri-o are two of them. Container images built with Docker can be run with either of these without anyone noticing.
The part of Kubernetes that runs containers has had a shim for docker along with an interface for runtimes to use. It's called the Container Runtime Interface (CRI). The docker shim that worked alongside CRI is being deprecated and now all runtimes (including Docker) will need to use the CRI interface.
These days there are numerous container runtimes one can use. containerd and cri-o are two of them. Container images built with Docker can be run with either of these without anyone noticing.