Google says "Google hasn't verified this app" when I connect. Is it safe?

Yes, it is safe to continue. While Google is still reviewing Playbox’s access to YouTube and Google Calendar, its sign-in screen may show “Google hasn’t verified this app”. Tap Advanced, then “Go to play-box.xyz”, and allow access. The warning is part of Google’s review process, not a problem with your account, and it goes away once the review is finished.

Playbox asks only for what each connection needs: for YouTube, managing live broadcasts on the channel you choose; for Google Calendar, creating and changing events in calendars you own, used only for your games. You can take access back at any time: tap Disconnect in Settings → Connected Apps, or remove Playbox at myaccount.google.com/permissions. Removing Playbox in your Google account stops both streaming to your channel and calendar sync for that Google account until you connect again.