I just recently got a new laptop with Windows 11 and found that the tabs in Opera browser were too small. I reached out to Opera and got no suitable answer and decided to try and find answer in Windows settings. Right clicked on Desktop and stumbled around awhile then clicked on Accessibility and changed Text Size which changed both the Opera tab font size and the page font size, so I left the text size the same that I had changed in the Accessibility section of Settings then went back to Opera page and used Control - to change the page font size and the tab font did not change. Hallelujah!