M321R4GA3EB0-CWM is a Samsung ddr5 rdimm.
A DDR5 registered DIMM carries buffered memory modules for servers, with on-module power management.
It is used in servers and data centre systems, where the part has to hold its specification over the life of the equipment.
Within the family, this ordering code is the one specified for 5,600 Mbps per data pin (equivalent MT/s) data rate.
The closest other ordering code is M321R2GA3EB0-CWM, which differs in capacity (16 GB against 32 GB).
Its Memory Technology is stated as DDR5 SDRAM in the data sheet.
The reason to choose it is the fit between the specification and the function it performs on the board.