On Mac, you may need Cmd. It's also possible your shortcuts have previously been customized. But the menu item Tools / Remove Selected measures should always work. If you continue to have trouble, please attach your score and give the precise steps to reproduce the problem (eg, tel us which measures you are selecting, which specific command you are trying).
Comments
You are probably doing something wrong.
Do you have a measure selected? There will be a blue box around it.
On Mac, you may need Cmd. It's also possible your shortcuts have previously been customized. But the menu item Tools / Remove Selected measures should always work. If you continue to have trouble, please attach your score and give the precise steps to reproduce the problem (eg, tel us which measures you are selecting, which specific command you are trying).
Might be a duplicate of #322965: Mac: Cmd+Del doesn't work to delete a measure in a score