We've had early feedback from the M3 release that the repackaging of EnvironmentPostProcessor causes some upgrade pain, especially for library authors who might have otherwise been able to get away with supporting Spring Boot 3.5 and 4.0 in the same release.
It might be possible for us to reintroduce the older class in a deprecated form if we're happy to live with the package tangle for a while.
Comment From: philwebb
Here's a sample that shows the problem: https://github.com/philwebb/gh-47272-sample Here's one possible fix: https://github.com/philwebb/spring-boot/tree/gh-47272