Recently, I purchased the breakout board for my Portenta C33. I am unable to compile any programs for the C33 due to the Breakout library being made for MBED Portenta boards:
fatal error: mbed.h: No such file or directory
#include <mbed.h>
How can I solve this issue? The documentation for the C33 does mention being compatible with the breakout board.
As you noticed, at this time the Arduino_PortentaBreakout library is only compatible with the Portenta H7 family of boards.
You can still use the Portenta Breakout with the Portenta C33 board, but you'll need to do without the library. The library provides a convenient interface for writing code using the breakout board, but it not in any way required in order to use the breakout.