Core Tunnel runs an external ssh — and it's resolving to Apple's /usr/bin/ssh, whose ssh-sk-helper has no libfido2.
I tried setting the PATH env var to make Core Tunnel resolve ssh to my MacPorts build (which reaches its own FIDO2-capable ssh-sk-helper), but this did not work.
Is there, or can there be, a way to choose an ssh backend to use?