Mac keyboard typing the wrong characters? Check the input source

If the menu is hidden, open System Settings → Keyboard. Under Text Input, click Edit and turn on Show Input menu in menu bar. Use the menu to choose the layout you need. If it is missing, add it from the same Text Input settings.

Choose Show Keyboard Viewer from the Input menu. Find the problem key by position. If it produces the wrong symbol only with Shift or Option held down, hold that modifier on your physical keyboard while Keyboard Viewer is open to see that version of the layout. Try typing the symbol in a blank document.

If the input source changes when you return to a document, check Automatically switch to a document’s input source in the Text Input settings. With this option on, a document can keep using the input source you chose for it until you close it. Turn the option off if you want to choose the layout yourself when switching documents.

If Keyboard Viewer shows the expected layout but the app still types a different character, try the same key in a blank TextEdit document. A mismatch in only one app narrows the search to that app. If one external keyboard has the problem across apps, compare it with the built-in keyboard or another keyboard using the same input source.