> 1) the datasheet "Rev. 2.6 - 3 September 2020" says that the maximum speed is 150MHz.
> 2) The user's manual UM10914 "Rev. 2.0 - 9 May 2018" says that the maximum speed is 100MHz.
The MCU version might have changed in the meantime, perhaps check the schematics.
> if I try to set something faster than 120MHz with mcuxpresso_v3.01.000 libraries, the M4 goes in Hardware Fault exception.
Flash interface settings are tightly related to core speed. The higher the core clock, the more wait states you will need for the slower Flash. Too tight setting will lead to crashes and hardfaults.
You might need to check the MCU user manual, and change your SDK example accordingly.
I rarely mess with the core clock settings, haven't done it myself on a LPC.