Linux

The only reason ssh client would "hang" without any output is when it's waiting for external key storage to allow access. It's designed that way to give user some time to approve access to key storage.

It sometimes happen that the installed key storage is broken in a way that it fails to show user modal, for any reason (showing on wrong screen, wrong desktop, wrong activity, wrong framebuffer, ....)

One solution (that you already did) is to change the SSH agent env variable to point to different key storage.

Another would be (if possible) to uninstall the broken key storage if you don't use it. But it is sometimes needed/used by other apps.

It's overall good to notify/open bug on your distro issue tracker to notify that some packages are missconfigured (maybe have missing dependencies) or conflicts with other ones.

What happens if you run commands on that blinking cursor? E.g. it you run ls do you get an output? I've had that happen in the past, don't remember the reason though.

I am not sure I "solved" this but when I add this to my startup script for my terminal (~/.zshrc):

SSH_AUTH_SOCK=/tmp/ssh-agent-$USER-socket
export SSH_AUTH_SOCK

it works then. I am not sure I'm still using the ssh agent, but at least it also does not cache my passphrase (or private key in ram)

I have no idea why but ssh seems to not use keys with different names by default

Your shell for user pi may be broken. Try adding the shell command to your ssh command explicitly like

ssh pi@host /bin/sh

Or use /bin/bash

@dysprosium ssh agent manages your ssh keys and automatically passes them as an identity when connecting to a server

If you want to connect without it, you can simply pass -i \<path to private key\> flag