so is Opera (on linux).. some 3-4px artificial frame-of-theirs that does not come or be controllable by window-manager. Why? To look rounded on rounded phones? All these "pink-fluffy-unicorn" looks-feels of all recent techie stuff start to make me sick..
I'm happy with the rounded corners in Opera (although I rarely see them since I leave the window maximized most of the time); in face, I would love to see KDE Plasma adopt the same strategy of rounding all four corners of windows. It looks nice, and Windows 11 has reinforced that it can work fine without getting in the user's way (although Windows 11 rounded them too much, and now it's hard to resize windows easily).
Only if it can be disabled. I would hate this quite a lot.