I tried both the registering and the login with elinks, and it didn't work. I did try try NeonModemOverdrive, but for example the inability to start new conversations was quite a show-stopper. (what you can do, however, is to start a conversation using Mastodon with one account, then continue that conversation with NeonModemOverdrive, on another account. That's necessary because Mastodon is lacking some features in its Lemmy-support as well – some messages or parts of messages fail to show properly on it.
I now tried installing just the basic links from the Ubuntu repository instead of elinks – and the login doesn't work either on Sopuli or on lemmy.sdf.org . How have you managed to get that to work?