I don't know why your Opera browser won't let you use any Google docs. After all, Sheets, Calendars, and Office Word can be downloaded and installed as an Opera browser extension without any problem. Try finding these extensions in the Opera Extensions Store. If you can't install it, remove the restriction on using Google content in Opera. What search engine are you using? I guess it's definitely not Google. Until you find a solution to the problem with Google syncing calendars, you can download a calendar template from 123calendars.com to use in any program you choose where you can edit JPG, PNG, or PDF files. You can easily find solutions to your problem or find alternatives. Good luck.
