Modifier keys on Linux. Ctrl covers most actions: tabs, find, print, save, zoom, text editing. Alt covers page-history navigation, window cycling (Alt+Tab), and Preferences (Alt+P). Super appears once, for minimizing a window (Super+M on most desktop environments).
Desktop environment can intercept a shortcut. A few window-level bindings, like minimizing with Super+M or cycling windows with Alt+Tab, are handled by your desktop environment (GNOME, KDE, and others) rather than Opera itself, so behavior can vary slightly by distro and DE.
Advanced keyboard shortcuts. Once enabled in Settings, the single-key zoom shortcuts use the 0 and 9 digit keys, matching the Windows layout rather than the bare + and - keys Mac uses.