SAMSUNG M471A1K43CB1-CTD 2666MHz Memory Modules (8GB, 1 x 8GB, DDR4, 2666 MHz, 260-Pin SO-DIMM, Black, Green) at Amazon.com
OWC 32GB (2 x 16GB) PC21300 DDR4 2666MHz SO-DIMMs Memory, Compatible with Mac Mini 2018, iMac 2019 and up, and Compatible PCs, (OWC2666DDR4S32P) at Amazon.com