Context. Cygnus X is one of the closest and most active high-mass star-forming regions in our Galaxy, making it one of the best laboratories for studying massive star formation. Aims. We aim to investigate the properties of molecular gas structures on different linear scales with the 4.8 GHz formaldehyde (H 2 CO) absorption line in Cygnus X. Methods. As part of the GLOSTAR Galactic plane survey, we performed large-scale (7º×3º) simultaneous H 2 CO (1 1,0 –1 1,1 ) spectral line and radio continuum imaging observations toward Cygnus X at λ ~6 cm with the Karl G. Jansky Very Large Array and the Effelsberg 100 m radio telescope. We used auxiliary HI, 13 CO (1–0), dust continuum, and dust polarization data for our analysis. Results. Our Effelsberg observations reveal widespread H 2 CO (1 1,0 –1 1,1 ) absorption with a spatial extent of ≳50 pc in Cygnus X for the first time. On large scales of 4.4 pc, the relative orientation between the local velocity gradient and the magnetic field tends to be more parallel at H 2 column densities of ≳1.8×10 22 cm −2 . On the smaller scale of 0.17 pc, our VLA+Effelsberg combined data reveal H 2 CO (1 1,0 –1 1,1 ) absorption only towards three bright H II regions. Our observations demonstrate that H 2 CO (1 1,0 –1 1,1 ) is optically thin in general. The kinematic analysis supports the assertion that molecular clouds generally exhibit supersonic motions on scales of 0.17−4.4 pc. We show a non-negligible contribution of the cosmic microwave background radiation to the extended absorption features in Cygnus X. Our observations suggest that H 2 CO (1 1,0 –1 1,1 ) can trace molecular gas with H 2 column densities of ≳5 × 10 21 cm −2 (i.e., A V ≳ 5). The ortho-H 2 CO fractional abundance with respect to H 2 has a mean value of 7.0 × 10 −10 . A comparison of the velocity dispersions on different linear scales suggests that the velocity dispersions of the dominant −3 km s −1 velocity component in the prominent DR21 region are nearly identical on scales of 0.17−4.4 pc, which deviates from the expected behavior of classic turbulence.< Réduire