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
Results:
The Decal and Post Process material do not adapt with the exposure changes like the Lit and Unlit materials on the Cubes.
Expected:
All of the materials would adapt with the exposure changes.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-73278 in the post.