This message only shows up in Brazil, and it's been like that since Runescape was officially launched in Brazil. I think if you're not in Brazil, the only way to see this message is to use a VPN. Thankfully, this issue has been fixed. I don't know when it was fixed, probably in the last 8 months. The annoying warning still shows up, but the bug has been fixed.
It had been like that for years, even on mobile. I've been using firefox, but the issue happened in chromium-based browsers, including google chrome, opera and brave.
13-Mar-2022 18:21:41