How to understand a microcontroller's name?
Each manufacturer labels its parts however it likes, usually explained on the datasheet or ordering information of its web site.  For this particular part, a STM32F407VG is in a 100-pin package (V) and has 1024 Kbytes of memory (G).

From the ordering page of the datasheet:


From STM32 datasheet https://www.st.com/resource/en/datasheet/stm32f407vg.pdf