The linked datapack is supposed to change the nether height to be 256. I do this by changing the logicalHeight value from 128 to 256. This does not work.
This datapack also adds overworld sky to the nether, that is part of bug report MC-197337
How it should work:
The nether height should change to be 256 blocks height.
Thank you for your report!
However, we are already tracking this issue, and this report is a Duplicate of MC-187716, which is a report that has not been resolved yet.
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