Vivaldi Calendar checks for updates from the online calendar accounts you’ve added to Vivaldi every 10 minutes. You can also trigger updates manually. When you have single-key Keyboard Shortcuts enabled, the easiest option is to just press the R key and you’ll be up to date.

In true Vivaldi fashion, there are other ways to update the calendar:

• In the main Calendar view, open the Calendar’s menu in the top left corner and select “Refresh”.
• Click on the Calendar button on the Status Bar, go to the Accounts tab, and click “Refresh”.
• Type “Refresh Calendar” in Quick Commands.
• Create a Mouse Gesture for the action.