Hey, thanks for the detailed report, it really helps.
Short answer: the Connect via SSH dialog currently expects either user@host or an alias from ~/.ssh/config. Parsing a full CLI string like ssh user@host -p PORT -i KEY isn’t supported right now, and that’s bad because with that input there’s no error and no logs, the dialog just silently ignores it. It feels broken. I’ve filed an internal report.
Your workaround adding a Host entry in ~/.ssh/config with HostName, Port, and IdentityFile is the recommended approach for now, and it also gives you an alias in the dropdown. Another user reported a similar symptom for non-default ports here: Unable to connect when ssh is running on other ports than 22, same root cause.
I can’t give an ETA for a fix, but at minimum the silent failure with no feedback should be validated and show a clear error. If I get updates, I’ll post them in the thread.