No, see Apple recommendations for upgrading RAM on iMac (Retina 5K, 27", 2019):
Use SO-DIMMs (Small Outline Dual Inline Memory Modules) that meet ALL of the following criteria:
- PC4-21333
- without buffer
- without parity
- 260-pin
- DDR4 SDRAM with 2666 MHz
https://support.apple.com/de-de...
PS:
Number of memory slots....4
Base memory......8 GB (two 4 GB DIMMs)
Maximum memory.....64 GB (four 16 GB DIMMs)