Are the indentation rules for multi-line round brackets weird, or am I doing something wrong in my configuration? Code formats like this:

return (
 foo
  ) as Something

which looks ugly compared to:

return (
 foo
) as Something

That seems like an issue to me. But probably that's an issue on ktlint. Could you check if you can reproduce it with ktlint? If so I recommend to open an issue there.

You can run ktlint on a file directly without gradle. Alternatively there might even be a ktlint docker image somewhere out there

To close the loop: upstream reports that this is the default behavior of the IJ formatter, and so the behavior of ktlint is intentional to match.