Largely self explanatory... I clicked a text that said "Want to get your own realm?" and a window appeared, normal. Splash offers redirect to webpage (Chrome, in my case) and does not go away, cannot be closed.

Have tried:

• Exiting current instance, restarting from new launcher: the window remained
• Restarting computer, then running instance: the window remained
• Changing GUI scale
• Clicking outside the "buy a realm" splash
• Clicking "Buy a realm!"
• Turning "Realms Notifications" off