Where is the "slice" button in Cura?
If auto-slicing is disabled, the button in the bottom-right corner of the window toggles between "Prepare" and "Save to File" depending on whether the model needs to be re-sliced or not. While slicing is in progress, it changes to "Cancel".

If auto-slicing is enabled, the button always reads "Save to File", and is greyed-out when slicing is being performed (it does not change to "Cancel").