CONFIG_PAGE_OFFSET_80000000 is not available for thedefaultarchitecture x86.
Result is shown for architecture csky

PAGE OFFSET 2G (user:kernel = 2:2)

configname: CONFIG_PAGE_OFFSET_80000000

PAGE OFFSET
└─>PAGE OFFSET 2G (user:kernel = 2:2)
In linux kernel since version 5.2 (release Date: 2019-07-07)