Since the Xbox Insider Hub app is unresponsive I figured I'd help share some information in case it might help alleviate the concerns of some users who managed to click a Join button but are unsure if they got in:
1. PSO2 New Genesis Closed Beta shows up in Preview tab
Clicking this loaded a new page.
2. Summary page and Join button
A long description mostly sharing some text with the website announcement with a Join button at the bottom. This button alone was probably not sufficient to get into the closed beta, as it loaded a popup on top:
3. Confirmation screen
A simple large popup with Cancel and Continue buttons. Clicking this made the popup disappear and returned to the Summary page from step 2 with the Join button greyed out. Some users reported it saying "Pending" at this point.
If this page loaded, the button changed to say Manage (which presumably gave the option to leave the beta). If it didn't, or if users clicked the back button in the top left, Xbox Insider Hub reverted to the main screen from step 1.
Confirming the above; the summary screen will update its Join button to say Manage.
3b. Manage popup
If you click the Manage button it'll open another popup. As expected this only provides an option to leave the beta. Do not click Leave preview. Just click Save - or ideally, don't click the Manage button in the first place because it doesn't help any!
4. Beta shows as Joined
Either way, if the app was still responsive, some users got to see the Closed Beta listed in the Joined section of the Previews tab. Clicking into this could get them back to the summary screen from step 2 with the Manage button, but by this point the app was pretty much dead to everyone.
What does this mean?
I expect anyone who saw the listing in the Joined section, and anyone who clicked the Continue button from step 3 and had their packet received before the Xbox Insider App died, have made it in. Moreover, anyone who did not make it to click that Continue button probably hasn't.
The question now is what this means. It's the Xbox Insider Hub that's collapsed under the weight of strenuous activity; it could be that the signups are nowhere near hitting the quota. This means that if and when the app starts working again, anyone present at the time may be able to join the beta still.
Sadly the only advice I can give on that front is to keep trying until either the app works again or Sega announce that signups are full so there's no longer any point in trying. And yes I know the former will contribute to the problem but sadly the nature of this means if you try to be generous and stop trying to get in, you'll increase your chances of missing out if there are still openings but only a few left.
Hopefully these screens are useful. Good luck everyone.