@speedylunar Try the steps in https://forums.opera.com/topic/23068/instructions-on-posting-about-problems-in-opera-for-computers
It doesn't seem to be happening here. Check also your video and monitor settings.
The way the links open is strictly up to the link author. AFAIK, no browser can override that behavior.
At some point, the "rel" tag may also affect links as browsers adopt the recommended behavior. rel=external is supposed to open in a new tab or window.