Geometrical and optical isomerism are both forms of steoreoisomerism, which is isomerism that arises due to difference in orientation in 3D space, and they are not mutually exclusive.
As per IUPAC, the strict definition of geometrical isomerism is
Stereoisomeric olefins or cycloalkanes (or hetero-analogues) which differ in the positions of atoms (or groups) relative to a reference plane: in the cis-isomer the atoms are on the same side, in the trans-isomer they are on opposite sides.
RS Nomenclature may be used to refer to the absolute configuration of a chiral molecule.
1,4-dichlorocyclohexane does not possess a chiral carbon, and you cannot use RS to denote the absolute configuration. It can however have cis and trans forms
1,3-dichlorocyclohexane has two chiral carbons, and 3 stereoisomers, 2 optically active forms which are enantiomers, and 1 optically inactive (meso) form
Using 'cis' or 'trans' here is not wrong, as it does satisfy the necessary conditions, but there are two 'trans' forms.