Choose your Platform: full shortcut list + printable PDF
Windows Ctrl is the modifier throughout: Ctrl+Alt+C to comment, Ctrl+B/I/U for text formatting. A few shortcuts (toggling the sidebar, panels, comments) use Ctrl on Windows too, avoiding a clash with browser shortcuts.
Mac Cmd covers most actions, but several use Ctrl instead to dodge macOS and Safari shortcuts, and text formatting (bold, italic, underline) uses Option rather than Cmd.