  In November 2021, Solar Orbiter started its nominal mission phase. The
remote-sensing instruments on board the spacecraft acquired scientific data
during three observing windows surrounding the perihelion of the first orbit of
this phase. The aim of the analysis is the detection of magnetohydrodynamic
(MHD) wave modes in an active region by exploiting the capabilities of
spectropolarimetric measurements. The High Resolution Telescope (HRT) of the
Polarimetric and Helioseismic Imager (SO/PHI) on board the Solar Orbiter
acquired a high-cadence data set of an active region. This is studied in the
paper. B-$\omega$ and phase-difference analyses are applied on line-of-sight
velocity and circular polarization maps and other averaged quantities. We find
that several MHD modes at different frequencies are excited in all analysed
structures. The leading sunspot shows a linear dependence of the phase lag on
the angle between the magnetic field and the line of sight of the observer in
its penumbra. The magnetic pore exhibits global resonances at several
frequencies, which are also excited by different wave modes. The SO/PHI
measurements clearly confirm the presence of magnetic and velocity oscillations
that are compatible with one or more MHD wave modes in pores and a sunspot.
Improvements in modelling are still necessary to interpret the relation between
the fluctuations of different diagnostics.
