In all beta versions of DF 11, the title bar buttons blinking and off and reappear after a while. They are also larger than the version 10. I have two monitors with different resolutions and scaling. In version 10, there is no such problem.

I did bigger tests. Until I launch the Vivaldi browser, everything seems to be fine. But after launching it, this happens...
Edit:
The "X-Mouse button" program makes the buttons disappear.
I have a setting for Vivaldi "Force scroll pages/lines...." there. If I turn this option off, there is no problem.

22:27:30

In the XMouse Button, create a profile for, for example, Notepad, and in this profile, under the Scrolling tab, set '4 Lines to scroll using the scroll wheel' and enable 'Force Scroll pages/Lines....'
Press Apply at the bottom.
From this moment on, when moving the mouse over the Notepad window, the buttons on the TitleBar will appear and disappear (all windows).
These symptoms do not occur in the older version of DisplayFusion.

It’s also possible that it’s a problem with the X-Mouse Button program that doesn’t cooperate well with the new version of DisplayFusion, particularly regarding the '4 Lines to scroll using the scroll wheel.' The default profile in X-Mouse Button is set to 3 lines. I’m thinking that when it detects the Notepad window and switches the settings for that profile, it may be causing these 'glitches.'