
Opera browser that was previously based on Presto, now using Blink/Chromium, is known to offer unique and innovative features such as Crypto, workspaces, pinboards, browser VPN, lacks basic Reader Mode feature. Finally, Opera Sofware is launching it with Opera 81 for Windows, Mac, and Linux, available in the dev channel as of now.
Reader Mode
These days, all modern browsers such as Firefox, Microsoft Edge, and Vivaldi come with Reader View, of these, Microsoft Edge has a better Immersive Reader, as it got features of Edge Legacy.
On the other hand, Google Chrome on desktop officially hasn’t launched Reader Mode, it is behind the flag for some time, not sure when it will be available to the public.
Opera for Android comes with Reader Mode, but not the desktop version.
Opera is finally offering the feature to let you read clutter-free text on web pages in a focused environment

How to use Reader Mode in Opera on Desktop
1. Visit an eligible webpage, when the book icon appears in the address bar, click on it
2. This loads the web page in a readable format.
3. You can improve your reading experience even further:
Click on customize appearance, select font from Sans-serif, Serif, and Monospace, choose a dark theme or sepia or continue using the default, drag the slider from small to large until you feel comfortable with text size on the screen.

To exit Reader Mode, click on the book icon in the address bar again.
As of now, for Reader Mode, Opera doesn’t offer keyboard shortcuts, menu options, and settings, expect them to appear in future updates.
The feature is available by default in the Dev version, here is how you can enable it Opera 79 stable version.
How to Enable Reader Mode in Opera stable now
1. Visit opera://flags/#enable-reader-mode
2. Select Enabled from the drop-down and restart Opera browser.
3. Visit a supported webpage, click on Opera menu >Page > toggle reader mode
You can access the Reader mode styling menu by clicking the A icon.
The Opera Reader Moder features are powered by Dom Distiller, which Chrome uses for its Reader Mode.
Opera shows a book icon in the address bar when a page supports Reader mode, you can exit by clicking the same icon.
More on Opera:
Opera 76 gets a feature to reduce duplicate tabs and other improvements
Enable or Disable Tab Snoozing in Opera browser
Opera 74 adds Native Chrome Web Store extensions installation support
Opera browser gets Music Player in Sidebar; Supports YouTube Music, Spotify, and Apple