That option is not enabled, If you can see whole snapshot I provided, I have highlighted that I could not change that option.
I have no clue why for some options are not enabled, One more example of this kind is, here I am attaching a snapshot of "MFA Interactive.svf"(example provided by Qlik), In this pie data labels exists even though nothing such as enable/disable exists in properties.
The option is located in the Properties panel on the right under the Appearance Tab, under the Presentation sub-tab: It is labeled as Value labels.
For a pie chart:
Please verify that this is what you see OR do not see - if you do not see this - or if it appears "disabled" please attach a screen shot of the issue.
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