I am trying to create data validation dropdown from a single cell which has all , separated values and I am splitting them using SPLIT(K4,","). But when I apply the formula drop-down just goes away. Here is how it looks:
And here is where I have applied validation:
It just happens and I can't see any drop-down here. Even validation doesn't work as I type a value from given values, it still identifies it as invalid:

Here it says that it is actually not possible, but otherwise, my data column will grow very big, that's why I wanted to keep it in a single cell.
Method to reproduce: Just make a copy of this sheet and experiment on your own whatever you want it to be like:

