The beta is open to anyone that has a Quest 2 or Quest Pro and has installed the latest Meta Quest updates. Roblox got an Open Beta VR app that's available now to Meta Quest 2 and Quest Pro HMD users.

Roblox RBLX announced that it is coming to Meta Platform ’s META Quest virtual reality (VR) Headset 2 and Pro, starting with an open beta , which will hit Quest’s App Lab in the coming weeks ...

You and others will also have access to a large, new library of content on Meta Quest devices. In the coming weeks, the makers of Roblox will release an open beta on Meta Quest’s App Lab.

Check the box beside Always allow www.roblox.com to open links of this type in the associated app, and click on Open Roblox It should fix the issues you are facing with the white screen on Roblox.