This article outlines the compatibility of the M300 and M350
Old and new generation accessories are pretty much fully compatible between the M300 and M350. However, it is very important not to mix and match accessories. Do not use a variety of different propellers, or batteries when operating either aircraft. All batteries and propellers should match. Note that you do need to update the firmware for some compatibilities to work. For example, the M300's firmware will need to be updated so it can be compatible with the DJI RC Plus.
The M300 Smart Controller is not compatible with the M350
A more in depth compatibility sheet can be found here: https://dl.djicdn.com/downloads/matrice-300/20230518RN/Accessory_Compatibility_List_for_M300_RTK_and_M350_RTK_EN.pdf