Which property file holds the setting of "Incrementally type" ?

It's in project's .idea folder, see https://i.imgur.com/xz45nW4.png

I have tried to change the type from IDEA to Zinc, but that property value was not updated(still "SBT").

If this property value is used to set the incrementally type, how do you internally distinguish between IDEA and Zinc?

SBT = Zinc. 

If the file exists and SBT is defined here, the option is set to Zinc. If the file does not exist, or there is no appropriate node in XML, IntelliJ IDEA sets the default (IDEA)

What I have in .idea directory is the following.

I have scala_compiler.xml with incrementalityType set to SBT, but the incrementally type shows IDEA not Zinc when I open the project

 scala_compiler.xml

<?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
   <component name="ScalaCompilerConfiguration">
     <option name="incrementalityType" value="SBT" />
     <profile name="mill 1" modules="...

Can't reproduce that locally. Once IDEA is set, the value is removed: https://i.imgur.com/uL50vrC.png

Try to reopen the project, there is a possibility that IDE stores the setting in RAM until restart. 

Restart does not help. The value(SBT) is still persists after restarting.

Is this some kind of bug if restarting or reopening the project does not remove the value?

And also it kind of weird that the value is still set to SBT but the incrementally type settings shows "IDEA".

Is it possible to reproduce that on a new Hello World project? 

I have figured that this behavior is happening only in my environment(this did not happen to my colleagues environment).

Thank you for your help.