The documentation mentions that canal is set as the default CNI, but I've noticed that canal (https://github.com/projectcalico/canal) seems to be long forsaken abandon-ware. Is there a fork that is used?

Not a direct answer to your question... But for RKE2, you do not have to use canal... https://docs.rke2.io/networking/basic_network_options#select-a-cni-plugin

I noticed that as well. I am trying to find the simplest solution to encrypt the traffic between nodes (running nodes from laptops on an untrusted network), the flannel configuration didn't seem to support the wireguard backend. Probably just better to use k3s.

As that project site says, canal is just calico+flannel, both of which have their own separate projects which are very much alive. The canal “project” was just manifests for deploying them together. RKE2 uses its own chart for that, which is maintained here: https://github.com/rancher/rke2-charts/tree/main-source/packages/rke2-canal/charts