The fade out parameter isn't working, I tested Fade in and is working as intended but Fade out no dice and that parameter is crucial for day night transitions. I am using 1.17.1 Fabric Java Edition...

You can put any value at "startFadeOut" and "endFadeOut" and the texture will just disappear when it reaches the endFadeOut tick value...

I am not able to reproduce this issue, and have not heard of it happening for others. I am going to close this issue now, if it still persists on the latest release for you please reopen the issue and post a skybox file that causes the problem.

OK I will install a new 1.18 server and report back, I was sticking to 1.17.1 because a lot of mods I use don't have support for 1.18 yet...

1.17.1 is not fully supported. Can you test In 1.18 and if the problem persists post your skybox file?

You could use viafabric which would allow you to join older servers