Hello, with Ardour-7rc2 al menu opens to the right side even if you are near the right screen border. With 2 monitor setup, menu are half way between monitors.
This does not happens with Ardour-6.9, where, when needed, menue opens to the left.
Which is odd, since both 7.0 and 6.9 use exactly the same GTK+ version, and menus are created and placed by GTK.
Is this a NVidia card? You can configure seamless screens there. – I cannot reproduce the issue (debian/mate-desktop, intel graphics). Even when stretching Ardour’s main window across two screens, context menu correctly stays on one.