Soil moisture giving false values when connected to 74hc4067 16 channel multiplexer

You’ve deleted all of the board types from the example sketch, rather than un-commenting one of them, so the custom board type will be in use.

That means you have a pin conflict caused by Settings.h, unless you’ve changed the default custom board type definition.

You should read the "Defining your physical switch and LED` section of this post…

Pete.