Q: How to set the file order (arrangement) permanently in Finder? I use High Sierra and each time I have to set the file order to "Date modified" but then the next time it defaults back to "None".
Any way to set it permanently for all folders?

A: All folders except the Applications folder and its sub-folder will maintain your setting for Date Modified if so set in the 

Arrange pull down menu



The Applications folder does not even has such a option.
However, if you're talking about the "Sort By" option, when you're in a folder press command+J to see the View options. 
Now go about setting the view options exactly how you'd like them to be. Once completed, click on the Use as Defaults button at bottom centre of the View options window. This will set your configuration as the default for all folders.
