Titular bishops have office, but no ordinary jurisdiction:
"According to the present
ecclesiastical discipline no
bishop can be
consecrated without title to a certain and distinct diocese which he governs either actually or potentially. Actual government requires residence, potential does not. Hence, there are two principal classes of
bishops, the residential, or
diocesan or, local, or ordinary; and the non-residential, or titular. Diocesan
bishops have and exercise (de jure) full power of order and
jurisdiction, in and over the diocese committed to their exclusive care by the
pope. Titulars, as such, have not, and do not exercise, power of order and
jurisdiction, in and over their
titular sees."
https://www.newadvent.org/cathen/02145b.htm