To fix the Twitch buffering issue on Opera, you should:

1. Check your network condition: make sure it is well-connected and strong enough.
2. Change your DNA to Google’s DNS if possible.
3. Update your browser to the newest version, or simply uninstall and reinstall your Opera.
4. Clear cache and cookies of your browser.
5. Disable the extensions or addons on your Opera.
6. Turn off Hardware Acceleration of Opera.
7. Switch to a more powerful VPN if you are using one to surf the Internet.

If you have done the above jobs to your Opera browser, but nothing changes, you can also try the following methods found online:

1. Change your browser: there are many browsers you can choose from including Chrome, Firefox, IE, etc.
2. Close the unused background applications on your computer.
3. Upgrade your computer's hardware for HD/4K streaming.

Resource: https://bit.ly/3xuLgNT

@stevejones
On the browser side, the solutions are quite similar to solve YouTube video not working problems on Chrome or Firefox like YouTube black screen, YouTube not responding, YouTube down, etc. To solve the error in Opera, you can refer to the following ways:
1. Make sure your network is working, and strong enough.
2. Disable hardware acceleration.

• Click on the Opera logo and select Settings
• Scroll down all the way to Advanced and click on this option
• Then, scroll down to System and toggle off the option Use hardware acceleration when available
  3. Disable the extensions and Opera’s built-in VPN
  4. Delete cache and cookies
• Click on the Opera logo in the upper left-hand corner and select History
• Click on Clear browsing data
• Select the time range and check all the three options to clear the browsing history, cookies, and other site data, as well as cached images and files
• Hit the Clear data button, close and restart Opera and check if you can now play the video that initially gave that media error.
  5. Reset browser settings or reinstall Opera
• Click on the Opera logo and then select Settings → Advanced
• Scroll all the way to the buttom of the page and click on Reset settings
• Click on Restore settings to their original defaults and hit the Reset button.