This problem is likely caused by a lack of support for anything newer than
TLS 1.0 in C-Kermit regardless of which version of OpenSSL it's built with.
I've fixed this in C-Kermit for Windows which connects to telnetd-ssl in
sid just fine negotiating a TLS 1.3 connection. I expect this change, along
with SSL improvements from some other people, will appear in
C-Kermit 10.0 beta.05 at some point.