Opera Mobile Emulator for Windows no longer available?

Yes, that's not just you.

People at Opera forums discovered a direct link to the Windows version: http://www.opera.com/download/get.pl?sub=++++&id=35131

Considering that the link in the article on this topic has no mention of the Opera Mobile Emulator, I concluded that the desktop version is no longer supported. However, all major browsers have a built-in mobile emulator in the developer tools.

For Opera, these are the steps to access it:

• Select the tab with the web page to be tested
• Open Menu > Developer > Developer Tools or CTRL + SHIFT + I
• Select the "Toggle device toolbar" icon at the top left (looks like a phone next to a tablet)
• Select the device from the first drop-down menu on the toolbar. It will be "Responsive" by default, or the last device used.

It's a similar process on other major browsers, like Chrome, Firefox and Edge. Comparing to physical devices I'd say it's reasonably accurate for testing layouts. It doesn't have the latest phones like iPhone 12 at this time, but you can add a custom device by specifying the viewport height and width.

My understanding is that each browser tests how it would behave on its own mobile version, which means, it's best to test it on the developer tools on all supported browsers. On this topic, there are tips and links to commercial testing tools on the MDN article on cross browser testing. My main take away is test a lot, and fix or provide fallback solutions.