And this is exactly something that capability system can solve...for example capabilities can be used to implement player thirst mechanics, mana levels etc...
You see this?
https://github.com/LukasSchikirianski/JungleAddonsMod/blob/master/Jungle Addons - 1.16.1/src/main/java/com/lukas/jungle_addons/JungleAddons.java#L30
You see how it says bus=Bus.MOD?
That's the wrong bus for those events.
It seems to me that you are registering your block items multiple times (as poopoodice already guessed), in your event handler onRegisterItems and in your ItemInit class. Choose one of the two registration methods
Use the ConditionalRecipe system. You can add a condition to make it determine whether to allow based on the config, recommended you use data generators for this as the recipes are easier to create using that, especially conditional ones. However, you will need to reload the recipe datapack if you plan to change the config value on the fly during runtime.
Delete all the files mentioned in this block of the log (if they exist) and try again:
Splitter:
Input: C:\Users\Arslan\AppData\Roaming\.minecraft\versions\1.16.3\1.16.3.jar
Input: C:\Users\Arslan\AppData\Roaming\.minecraft\versions\1.16.3\1.16.3.jar
Slim: C:\Users\Arslan\AppData\Roaming\.minecraft\libraries\net\minecraft\client\1.16.3-20200911.084530\client-1.16.3-20200911.084530-slim.jar
Data: null
Extra: C:\Users\Arslan\AppData\Roaming\.minecraft\libraries\net\minecraft\client\1.16.3-20200911.084530\client-1.16.3-20200911.084530-extra.jar
Including data in extra
SRG: C:\Users\Arslan\AppData\Roaming\.minecraft\libraries\de\oceanlabs\mcp\mcp_config\1.16.3-20200911.084530\mcp_config-1.16.3-20200911.084530-mappings.txt
InputSha: 3d2cba3c97cb57dd3f2a048933cb32ef6abd4639
SrgSha: de180369283e7aafbb5694c4b8995a9c83fe0a95