Invoking Aria’s summarize feature will not work as currently described by Opera unless you are accessing it within the mobile version of the Opera browser. None of your suggestions are making any difference for the current desktop version of Opera. However, the issue has already been successfully addressed by BestCodes on the first response to my original post.

i.e. You can summarize a webpage using the Aria in-browser Command Line. From within the Windows based browser use Ctrl+/ (Cmd+/ on Mac) and then click the Tab key to switch to the Page Context environment. The Summarize Page feature will appear as an option once the Page Context prompt is displayed.

Update Browser: Ensure your browser is up to date.
Clear Cache: Clear your cache and cookies.
Try Incognito: Use private or incognito mode.
Check Terms: Review Aria’s guidelines for desktop use.
Contact Support: If issues persist, reach out to Aria's support team.
Let me know if you need more help!

Click on the Aria icon (typically found in the sidebar). If it’s not visible, enable the sidebar by clicking the three dots at the bottom of the sidebar and toggling Aria on.

if the "sidebar" isn't visible, ... neither are the "three dots" >__<
XDDD

On macOS, you should be able to show \ hide the sidebar with [control + command+ s] shortcut...

• To go to settings, press ALT + P or access it from the Opera menu in the top left.
• It's easier to search 'Aria' in settings. Regardless, it's not in the 'Features' section; the Aria settings are in 'AI services':
  
• Do Not use Aria in the sidebar. Aria currently can't get page context from there. Instead, CTRL + / (or CTRL + Shift + 7), then press Tab for page context and ask Aria to summarize the web page.
• Aria will not block your request (the Aria UI or AI model might refuse to answer, but Aria gets page data from the browser — if you can see the page, so can Aria).
• There aren't older versions of Opera that “kinda” support page context. It was supported in the version described in this blog post:
  https://blogs.opera.com/news/2024/03/new-ask-aria-ai-feature-drop-opera-one-page-context/

If you use AI to try to solve problems, you should at the very least make sure that the AI didn't lie to you.

Make sure Aria is enabled in your Opera browser. Go to Settings (or Cmd + ,), navigate to the Features section, and check that Aria is activated.
Open the webpage you want to summarize.
Click on the Aria icon (typically found in the sidebar). If it’s not visible, enable the sidebar by clicking the three dots at the bottom of the sidebar and toggling Aria on.
In the Aria chat interface, type something like "Summarize this webpage" while the page is open.

If Aria blocks your request:

Ensure you have granted permissions for Aria to interact with the webpage.
Check that your Opera browser is updated to the latest version, as older versions might not fully support the feature.

If the issue persists, it could be a regional or account restriction. In that case, try contacting Opera support for further assistance.

The weird thing is that Aria was previously suggesting other menus and functions that didn't exist in my computer's Opera browser, but did exist in my mobile version of Opera (both browsers were updated versions of Opera). My conclusion is that Aria wasn't trained on the most recent desktop computer version of Opera, but only on the mobile version.

Even stranger, After updating Opera on my Mac, Opera's new features page specifically prompted me to explore the Aria page summary feature. Though I followed the specific instructions outlined by Opera, it only resulted in unusual error messages. I guess the new page summary feature wasn't tested on all platforms.

Try pressing CMD + /, then press Tab to use page context, and tell Aria to summarize the page.