The Boolean setting of $FCTraditionalFormOutput
determines which output format type should be used in the notebook front
end when FeynCalc is loaded. If set to True, FeynCalc will
activate the TraditionalForm output. Otherwise, the
StandardForm output (Mathematica’s default) will be
used.
This setting only changes the output format of the current notebook, i.e. it is not persistent and will not modify the global options of Mathematica.
If unsure, it is recommended to set
$FCTraditionalFormOutput to True, so that you
can benefit from the nice FeynCalc typesetting for various QFT
quantities.
Overview, FCEnableTraditionalFormOutput, FCDisableTraditionalFormOutput.