iMac 2019 - upgraded w 2 extra ram and the speed dropped to 2400 MHz? | MacRumors Forums
Amazon.com: OWC 8GB (2 x 4GB) PC19200 DDR4 2400MHz SO-DIMMs Memory Compatible with Mac Mini (Late 2018), 27" and 21.5" iMac (Mid 2017), and Compatible PCs (OWC2400DDR4S08P) : Everything Else
OWC OWC2400DDR4S16P 16GB DDR4 2400 MHz SODIMM Memory Upgrade Kit (2 x 8GB) for iMac
DDR4 2400MHz PC4-19200 for Apple iMac 21.5" 18,1 & 18,2