  We present high-cadence photometric and spectroscopic observations of
SN~2020jfo in ultraviolet and optical/near-infrared bands starting from $\sim
3$ to $\sim 434$ days after the explosion, including the earliest data with the
10.4\,m GTC. SN~2020jfo is a hydrogen-rich Type II SN with a relatively short
plateau duration ($67.0 \pm 0.6$ days). When compared to other Type II
supernovae (SNe) of similar or shorter plateau lengths, SN~2020jfo exhibits a
fainter peak absolute $V$-band magnitude ($M_V = -16.90 \pm 0.34$ mag).
SN~2020jfo shows significant H$\alpha$ absorption in the plateau phase similar
to that of typical SNe~II. The emission line of stable [Ni~II] $\lambda$7378,
mostly seen in low-luminosity SNe~II, is very prominent in the nebular-phase
spectra of SN~2020jfo. Using the relative strengths of [Ni~II] $\lambda$7378
and [Fe~II] $\lambda$7155, we derive the Ni/Fe production (abundance) ratio of
0.08--0.10, which is $\sim 1.5$ times the solar value. The progenitor mass of
SN~2020jfo from nebular-phase spectral modelling and semi-analytical modelling
falls in the range of 12--15\,$M_\odot$. Furthermore, semi-analytical modelling
suggests a massive H envelope in the progenitor of SN~2020jfo, which is
unlikely for SNe~II having short plateaus.
