OK, there are 2 pieces to this:
1) A variety of ST processors are supported from MathWorks via STM32MAT and a couple MathWorks Support Packages (8 Nucleo boards, 3 Disco boards). If they match what you need, you should look into using them.
2) For any other boards (STM32 not covered by the support, SP5, or anything else), you can still use MathWorks tools to generate embedded C code for your algorithm, but then you manually import that C code into your existing IDE project and integrate it there, and use the IDE or ST Tools to download code and debug on the device. This will work for STM32Gx, STM32Hx, SP5, etc.
Option 1 is just a streamlined option 2. Option 2 is the "generic" use case, and MathWorks Embedded Coder provides many features allowing you to customize the generated code to work within your embedded system and your software project in your IDE of choice.
Cheers,
-Brian
