OS-dependent modifier. As with other Microsoft 365 web apps, the modifier key depends on your operating system: Command on Mac, Ctrl on Windows. The shortcuts are otherwise identical between the two.
Text formatting. Formatting shortcuts, bold, italic, underline, alignment, lists, work in Word for the web the same way as in the desktop app. These are the most reliably consistent shortcuts across all Word platforms.
Heading styles in the web version. The Ctrl+Alt or Cmd+Option heading style shortcuts that work in the desktop app may not be fully supported in the web version. The table above covers what is actually available.
Tracked changes in the web version. Word for the web supports tracked changes, you can enable tracking, view changes, and accept or reject them. The full keyboard shortcut set for tracked changes review is more limited in the web version than in the desktop app. For heavy review work, the desktop version (Mac or Windows) provides more complete shortcut coverage.
Browser shortcut conflicts. Common browser shortcuts that can interfere with Word web app shortcuts include closing tabs (Ctrl+W / Cmd+W), opening new tabs, and switching tabs. These are captured by the browser before the Word web app sees them. The table above notes the most common conflicts.