@আফতাবুজ্জামান Hello, thank you for reporting this bug! The special pag wants you to use no-prefix names. However, it looks there's a bug in the autocomplete mechanism, looking to the main namespace instead to the template one. As the form checks for existance of the template, it doesn't let you to add a page that's not suggested by the autocomplete, and as the suggestions are wrong, you're not allowed to add this template there.
I filled this autocomplete bug as T285748 to Phabricator. Since I'm not able to fix the cause, I also figured out a workaround, which you can see in T285750 in Phabricator.
Ad 1) Unfortunately, that's not possible via the form because of a bug. If you feel like it, you can try editing bn:MediaWiki:NewcomerTasks.json manually, or also I can do it for you. Alternatively, you can wait until the bug is fixed, and use the form then.
Ad 2) That's expected. We decided to start using Wikidata items as link IDs. It does not impact what the user sees, the link IDs only change what we the Growth team see as what link the newcomers click. This data helps us to understand newcomers better. That's also why it's not possible to change IDs in the form itself. Feel free to keep the edit in :).
I hope this helps. Do let me know if you have any other questions. Best,