https://macmagazine.com.br/wp-content/uploads/2020/11/18-tea...

This image shows it best.

The memory is on the same package as the SoC. (It's not on the motherboard.)

IIRC modern Apple devices integrate the memory into the whole SoC instead of making it separate on the board and replaceable. It's definitely not swappable like a DIMM or CAMM module would be. Can't find a photo of a decapped M4 chip to prove it, though...