In a predictive modular invariant flavour theory, correlations between quark and lepton observables are expected.
However, with the exception of GUT models, almost all previous studies have analyzed these sectors separately,
preventing a comprehensive investigation of their interplay.
This work, based on analysis presented in arXiv:2409.15823, discusses the results of a truly unified analysis of
quark and lepton observables within a modular flavour model based on the $2O$ symmetry, employing a minimal set
of 14 real parameters.

The results demonstrate that the model aligns well with experimental data under a normal neutrino mass ordering,
while also predicting other key leptonic parameters, including the Dirac and Majorana CP-violating phases,
(\(\delta_{\text{CP}}, \eta_1, \eta_2\)), the lightest neutrino mass (\(m_1\)), and effective neutrino masses
relevant to beta and neutrinoless double beta decay (\(m_\beta, m_{\beta\beta}\)).

A comparative analysis of separate (quark-only and lepton-only) versus combined (quark and lepton) fits reveals
distinct shifts in best-fit values and parameter spaces, emphasizing a nontrivial correlation between quark and
lepton sectors.
Notably, our study uncovers strong correlations between several observables, such as the strange-to-bottom
quark mass ratio (\(r_{sb}\)), which is negatively correlated with the three lepton mixing angles,
\(\delta_{\text{CP}}, m_1, m_{\beta}, m_{\beta\beta}\),
while showing positive correlations with \(\eta_1\) and \(\eta_2\).
These significant interdependencies, which are overlooked in separate analyses,
provide, in principle, testable predictions for ongoing and future experimental studies.