Regardless if I turn the automatic sorting on or off, I can't sort anything manually in my inventory. The game simply combines the stacks together and sorts the inventory as it pleases. Am I doing something wrong? It works in chests though.

Did you turn off both the game's built in autosort and the one from the mod?

Edit: What I mean is in game settings and using shift+x

Thank you for your prompt response! I did not turn off the game's built in autosort. The problem is that I do not find any option to do so. Would you be so kind as to tell me how to turn off the game's built in autosort? Thanks in advance!

I am not at the computer so I don't know exactly where the setting is, but I think it's under something like "general" and it is called "keep main inventory sorted" or something like that.

Ok, I just checked and it is under interface > interaction and is called "Always keep player's main inventory sorted".

Oh wow! Thank you very much for your incredibly fast response! It works!