How so? I could register even with enabling "Advanced Settings" (because by enabling "Advanced Settings" you will need to enter the details manually but suwako didn't provide them so I had to guess).

Here's what I had entered in Gajim:

Select server:
https://xmpp.076.ne.jp/

[x] Advanced Settings

Hostname: xmpp.076.ne.jp
Port: 5222
Type: START TLS

If you still have error it's likely you should check how you connect with Gajim/Dino. Launch them from terminal (just type gajim or dino-im in your terminal) to see specific error messages.

Also did you use containers (idk, maybe firejail or any kinds of "sandboxes"), or proxy (like tor) and configured it wrongly?

You can also check if you can use other providers (https://providers.xmpp.net/). If you still can't, you can try Hookipa's as they provide a registration web page.