A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
This might be caused by a macOS system shortcut conflict (usually the text-to-speech accessibility feature or a window management shortcut overriding Excel).
To resolve the shortcut conflict, click the Apple menu () in the top-left corner of your screen and select System Settings. Scroll down the left sidebar and click Keyboard, then click the Keyboard Shortcuts... button on the right. Review the categories in the left pane, particularly Accessibility and Services, and look for any shortcut assigned to Command + Shift + T (⌘⇧T). One possible cause is the Accessibility > Spoken Content > Speak selection shortcut, which may be assigned to this combination. Uncheck the box next to the conflicting shortcut to disable it, or double-click the shortcut to assign a different key combination. Click Done and try using Command + Shift + T in Excel again.
If you need to use AutoSum right away, there are several alternatives. You can use the legacy Excel menu shortcuts by pressing Control + (the backtick key below Esc), releasing the keys, and then pressing H, U, and S sequentially. Alternatively, open the Home tab on the Excel ribbon, locate the Greek Sigma symbol (∑ AutoSum) toward the right side, and click it. You can also enter the formula manually by typing =SUM(, selecting the range of cells you want to add, and pressing Enter.
If this doesn't resolve the issue, follow https://maccove.com/blog/why-excel-keyboard-shortcuts-dont-work-mac
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hth
Marcin