  A significant fraction of local galaxies exhibit stellar bars,
non-axisymmetric structures composed of stars, gas, and dust. Identifying key
differences between the properties of barred and unbarred galaxies can uncover
clues about the conditions for triggering bar formation. We explore the early
stages of bar formation in a small sample of disc barred galaxies extracted
from the TNG50 cosmological simulation, and compare their properties to those
of unbarred galaxies. According to our results, the most important difference
between barred and unbarred galaxies is that the former have systematically
higher fractions of stellar to dark matter mass in their inner regions, from
very early stages and prior to the formation of the bars. They harbour high
initial gas content, fostering increased star formation rates and leading to a
central mass concentration that grows faster over time compared to unbarred
galaxies. Examining the evolution of the halo spin within 10 ckpc reveals that
barred galaxies have higher angular momentum transfer from the disc to the
halo. Curiously, both barred and unbarred galaxies share similar initial low
values of the halo spin, consistent with those proposed in the literature for
bar formation. Furthermore, we evaluate existing stability criteria to capture
the complexity of the process, and investigate the effects of mergers, flybys,
and environment as possible drivers of bar formation. We find no clear link
between mergers and disc instabilities resulting in the formation of bars, even
though some of the simulated barred galaxies might have been influenced by
these events.
