トピックを開始する際にOneboxingが機能しない、情報が事前入力されている

[Falco]

IMO you are expected to encode any query unsafe query params,

@techAPJ

you can use w3Schools’s HTML URL Encoding Reference to find what text characters are encoded as in the URL, there is even a text to URL converter in the Try It Yourself section in the page linked above in this paragraph.

so

https://meta.discourse.org/new-topic?title=https://www.xkcd.com/556

becomes

https://meta.discourse.org/new-topic?title=https%3A%2F%2Fwww.xkcd.com%2F556

that works like Discourse Meta (open in a new tab)