How to tick the “Specify heat of reaction”?

Hello, developers,I would like to ask why I can’t I tick this option of “Specify heat of reaction”?
Looking forward to any possible answers! Thank you very much!

Are energy equations enabled?

There should be a pop-up message (‘tooltip’) explaining why disabled inputs are disabled, if you hover over the control.

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Yes, I have solved this problem with your help, thank you very much!