Turn on the option Use DNS-over-HTTPS instead of the system’s DNS settings.

On the right, scroll down to the System section.In Settings, click on Advanced > Browser on the left.Pressing Alt + P opens Settings directly. Click on the Opera icon to open the browser's menu.Here's what you have to do to get DoH enabled. Opera 67, the latest stable version as of the time of this writing, has a special option in Settings, so you no longer need to deal with flags. By that time, it was limited to the Cloudflare provider, and was an experimental option which had to be enabled with a flag. The DoH feature is available in Opera starting with beta version 65. It is intended to increase user privacy and security by preventing eavesdropping and manipulation of DNS data by man-in-the-middle attacks by using the HTTPS protocol to encrypt the data between the DoH client and the DoH-based DNS resolver. For those who is not familiar with DoH, DNS-over-HTTPS is a relatively young web protocol, implement about two years ago.

How to open opera settings