scp/rsync hangs when trying to connect to a very old Mac

I am trying to transfer files from an ancient Mac (OS 10.5.8) that has not been upgraded for years to a new (Ventura 13.3.1) machine and find that scp and rsync don't work. The old Mac is visible in my home network, and yesterday I was still able to transfer files with scp -r -oHostKeyAlgorithms=+ssh-rsa myuser@oldmac.local:Desktop/transfer . Today this didn't work anymore after trying unsuccessfully to rsync files from the new machine to the old one. rsync always hangs with no error messages (in spite of using -v), and scp now also simply hangs. What's going on, and how can I fix it and at least transfer files between the machines?