https://twitter.com/RuneScape/status/1334227093597679619?s=19
This is what the OP is referring to.
We're always looking for your feedback to help guide the future of our games, and this time, we need your help to improve our web experience! By taking part in research about our website, including how it looks and functions, you will help inform our future website development and make sure we're building a web experience that includes what's important to you!
We’ll need you to be:
· English-speaking
· Available on Thursday 10th December at 5pm for an hour or so to provide live feedback
Interested? Please fill out this short survey, which should take a couple of minutes, and we’ll contact you via email next week if you’ve been successful with the full details.
For those taking part next Thursday, we'll provide a Bond to your chosen account to thank you for your time. Thanks again!
Would you be interested in taking part in a 60-minute session at 5pm on Thursday 10th December to help shape the future of our website?
Might be a bit late to apply now though since the cut off isn't too clear other than "next week", which is now.
It should have been posted here too imo, however they may be approaching different audiences first and may very well plan to approach the forum audience separately. I've mentioned this to Community Management so hopefully they'll chime in and let us know.
Edit: the survey link is still open (assuming they plan to close it off at some point between now and Thursday) so you could try filling it in and seeing if you are successfully invited:
https://jgx.game/WebSurvey