What does 4xVDD and 4xVSS mean in STM32F302xB and STM32F302xC datasheet?
It means that the package of the chip actually has 4 physical pin pairs of VDD and VSS.
Each of these supply pairs should be properly connected and decoupled to supply all parts of the chip reliably.

Edit: Actually, the pair I marked on the left is the analog supply pair, which is shown separately in your schematic. So the package in my picture has only three of the digital supply pairs, but you get the point.