@opera-qa-team: hagerty.co.uk . I have JavaScript disabled on untrusted sites, and without JS the page load on this site never completes and a core stays at 100%. It's fine with JS enabled.

@thelittlebrowserthatcould: It must be a website causing this, I just saved the open tabs (many dozens) as a Speed Dial folder and then closed them all, CPU went back to normal. So doesn't look like an Opera bug after all. Now to establish which website!

Bug in 122.0.5643.142 on Linux, where a CPU core is constantly at 100%, whether Opera is the active window or not. Did not occur in the previous version. Top is showing one Opera process at 100% CPU and two others approx. 40%, this is with the browser window inactive! No videos or music playing, etc.