Question about MSI B450I Gaming Plus AC

240PIN is DDR3 and would be very unusual for DDR4 memory.
ALWAYS check the manufacturer's page of the board for memory. There you will find a list of the compatible RAM modules. You should stick to it pretty closely. My experience has taught me that sometimes even small deviations cause crashes. In the best case, you can get a stable state by reducing the clock rate in the bios.