TapNoiseWhen a shortcut does the wrong thing, first find out which layer is interpreting it. macOS, the front app, an editor extension and a keyboard remapper can each have bindings of their own.
Check the app’s menu
Bring the intended app forward and open the menu containing the action. If the command is disabled, satisfy its requirements, such as selecting text or opening a document. A disabled command will not become available merely because you press its shortcut.
Read the combination shown beside it. Your remembered binding may belong to another app, an older version or a different keyboard layout.
Isolate the competing layer
Test with the built-in keyboard if you normally use an external one. Check the active input source and Fn behaviour. Temporarily pause a remapping utility using its normal controls, then retry the same harmless action.
Inspect System Settings › Keyboard › Keyboard Shortcuts for a system action using that combination. Change one binding at a time and record the old value so you can undo the test.
Avoid adding another conflict
For a custom menu shortcut, use the exact command title and limit the entry to the relevant app. Do not overwrite common Copy, Paste or Undo combinations without a specific reason.
TapNoise’s shortcut sheet displays menu shortcuts, but it does not catalogue every extension’s private keymap. For a mapping problem on external hardware, see modifier key settings.
Source: Apple: use macOS keyboard shortcuts.