Error:

java.lang.NullPointerException: Cannot read field "bgR" because "io.github.a5b84.darkloadingscreen.Mod.config" is null

Crash report: https://pastebin.com/x9XyEUgY

Crash log: https://pastebin.com/vN18pU03

Couldn't reproduce but it should be fixed anyway now, feel free to reopen the issue if it's still not working

Now I get an Iris exception, but I don't know if it is related to the mod:

java.lang.NullPointerException: Cannot invoke "net.coderbot.iris.pipeline.PipelineManager.getPipeline()" because the return value of "net.coderbot.iris.Iris.getPipelineManager()" is null

I've digged a bit on previous version and it seems that the issue was some incompatibility with Flytre Lib v1 (I read it's a complete rewrite).
I can load the game without the Iris exception by disabling FlytreLib. However, with the previous version of Dark Loading Screen I didn't have that issue, although it was incompatible FlytreLib (disabling DLS worked)

I doubt this is caused by mod but I think it's because of another mod messing with other mods' initializers (mine was supposed to load the config but it wasn't called and crashed your game, I guess Iris' creates their PipelineManager)

I very vaguely remember people saying things about Not Enough Crashes and it does appear to do something with mod entrypoints here so I guess you can try removing it