Here is why LPDDR4x-4266 RAM seems considerably faster when coupled with Intel Tiger Lake-U CPUs compared to equivalent AMD Renoir APUs - NotebookCheck.net News
G.SKILL Announces New DDR4 Specifications for Intel Kaby Lake Platform - DDR4-4266MHz CL19 8GBx2 & DDR4-4133MHz CL19 8GBx4 - G.SKILL International Enterprise Co., Ltd.
G.SKILL 32GB (4 x 8GB) TridentZ RGB Series DDR4 PC4-34100 4266MHz Desktop Memory Model F4-4266C17Q-32GTZR at Amazon.com
Having trouble hitting 4266MHz DDR4 RAM speeds with AMD Ryzen 9 5950X