The Eye Adaptation material node only functions in Surface Material Domain.
Found in 4.20 CL# 4369336, 4.21 CL# 4753647, 4.22 CL# 5660361, and 4.23 CL# 6074473
The Decal and Post Process material do not adapt with the exposure changes like the Lit and Unlit materials on the Cubes.
All of the materials would adapt with the exposure changes.
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-73278 in the post.