  AGC 114905 is a dwarf gas-rich ultra-diffuse galaxy seemingly in tension with
the cold dark matter (CDM) model. Specifically, the galaxy appears to have an
extremely low-density halo and a high baryon fraction, while CDM predicts
dwarfs to have very dense and dominant dark haloes. The alleged tension relies
on the galaxy's rotation curve decomposition, which depends heavily on its
inclination. This inclination, estimated from the gas (neutral atomic hydrogen,
HI) morphology, remains somewhat uncertain. We present unmatched ultra-deep
optical imaging of AGC 114905 reaching surface brightness limits $\mu_{\rm
r,lim} \approx 32$ mag/arcsec$^2$ ($3\sigma$; 10 arcsec $\times$ 10 arcsec)
obtained with the 10.4-m Gran Telescopio Canarias. With the new imaging, we
characterise the galaxy's morphology, surface brightness, colours, and stellar
mass profiles in great detail. The stellar disc has a similar extent as the
gas, presents spiral arms-like features, and shows a well-defined edge. Stars
and gas share similar morphology, and crucially, we find an inclination of
$31\pm2^\circ$, in agreement with the previous determinations. We revisit the
rotation curve decomposition of the galaxy, and we explore different mass
models in the context of CDM, self-interacting dark matter (SIDM), fuzzy dark
matter (FDM) or Modified Newtonian Dynamics (MOND). We find that the latter
does not fit the circular speed of the galaxy, while CDM only does so with dark
halo parameters rarely seen in cosmological simulations. Within the
uncertainties, SIDM and FDM remain feasible candidates to explain the observed
kinematics of AGC 114905.
