Posted on May 03, 2018 at 22:35Hello Boghdan,
STM32L4 MCUs with extension 'P' like for example STM32L496ZGTxP are devices, that support external SMPS. The idea is to reduce current consumption of MCU by bypassing embedded LDO and providing Vcore voltage from external SMPS (DC/DC + switch). Such enhanced STM32L4 MCUs were created based on standard non 'P' versions of STM32L4 MCUs by making replacement of few GPIO pins with Vcore (VDD12) pins.
You are right that Keil MDK-ARM with up to date STM32L4 pack doesn't embed definition of STM32L4 'P' devices, including STM32L496ZGTxP, which is present on Nucleo kit. I faced this some time ago and my workaround was to open settings of Keil project and select new device - the same like the one I want to use but without 'P' at the end. In your case it will be STM32L496ZGTx. This solution should allow you to work with MCU, including access to periperals in debug session.

I am sorry for the inconvenience.
Regards
Szymon