I don’t think there is any abstraction library for STM32 in Keil MDK by default. The ARM toolchain provided by Keil is mostly for bare-metal programming. I am not familiar with Keil, so if I am wrong you can correct me.
STM32CubeMX is not a IDE. It’s a code generator software for the STM32 microcontroller. CubeMX has all the toolchains needed for the STM32 programming. Once installed, you can create a new project in CubeMx and you can open the project in Keil IDE. See the below video, to configure CubeMx with Keil.
Or, You may ditch Keil, and use STM32CubeIDE which is free and comes with an IDE and all the necessary tools for easy designing. See this video below, you will get an idea of, how to create a new project in STM32CubeIDE.