  The concordance of the $\Lambda$CDM cosmological model in light of current
observations has been the subject of an intense debate in recent months. The
2018 Planck Cosmic Microwave Background (CMB) temperature anisotropy power
spectrum measurements appear at face value to favour a spatially closed
Universe with curvature parameter $\Omega_K<0$. This preference disappears if
Baryon Acoustic Oscillation (BAO) measurements are combined with Planck data to
break the geometrical degeneracy, although the reliability of this combination
has been questioned due to the strong tension present between the two datasets
when assuming a curved Universe. Here, we approach this issue from yet another
point of view, using measurements of the full-shape (FS) galaxy power spectrum,
$P(k)$, from the Baryon Oscillation Spectroscopic Survey DR12 CMASS sample. By
combining Planck data with FS measurements, we break the geometrical degeneracy
and find $\Omega_K=0.0023 \pm 0.0028$. This constrains the Universe to be
spatially flat to sub-percent precision, in excellent agreement with results
obtained using BAO measurements. However, as with BAO, the overall increase in
the best-fit $\chi^2$ suggests a similar level of tension between Planck and
$P(k)$ under the assumption of a curved Universe. While the debate on spatial
curvature and the concordance between cosmological datasets remains open, our
results provide new perspectives on the issue, highlighting the crucial role of
FS measurements in the era of precision cosmology.
