Hello @MOhamed_Mehery,
First, VDD12 is only available on packages with the external SMPS supply option.
Also, it is not necessary to wire this pin, you can use it, if you want to improve the power consumption, especially in Run and Sleep mode.
In that case, there are 3 SMPS ranges to supply VDD12, please check RM0394 section 5.1.6
Hope that helps!
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