The tvOS 11.4.1 public beta can be obtained by going to the Settings app on the Apple TV and navigating to the Software Updates section under "System." "Get Public Beta Updates" will need to be toggled on, and once it is, the Apple TV will download the beta software.
No notable features or changes were discovered in the first two developer betas of tvOS 11.4.1, suggesting this is a minor update.
Most tvOS updates have been minor in scale, and Apple does not provide detailed notes outlining what's new, so we may not know just what's included in tvOS 11.4.1 if it's only bug fixes.
tvOS 11.4.1 is going to be one of the last updates to the tvOS 11 operating system with Apple now shifting its focus to tvOS 12.