The two processes are different.
The biggest difference between the 855 and 8gen1 processors is their different processes. The Snapdragon 855 mobile phone processor is a chip for a mobile processing platform released by Qualcomm in December 2018, using TSMC's 7nm process. The Snapdragon 8gen1 is a new generation of Qualcomm Snapdragon mobile platform, released in December 2021, using Samsung's 4nm process.