Aims. This study aims to identify very low-mass members within the Barnard 30 dark cloud, with a particular focus on detecting objects in the substellar domain, including those within the planetary-mass regime. Methods. We employed deep photometric observations using data from the Euclid mission, incorporating advanced data-processing techniques -- most notably, the DeNeb tool -- for optimised source detection. We also analysed multi-wavelength ancillary observations and performed a spectral-energy-distribution analysis for each candidate member. In addition, low-resolution near-infrared spectroscopy was obtained for one candidate to further assess its nature and properties. Results. Our initial photometric analysis yielded an initial sample of nearly 100 candidate members in the substellar mass range. A subsample of 23 probable members, located close to the 3 Myr isochrone, has been identified. We have thus substantially expanded the known population of faint, cool sources associated with the region. Low-resolution, near-infrared spectroscopic analysis of one candidate reveals an L2 spectral type with low gravity, consistent with a young, ultra-cool dwarf. If its membership is confirmed, its estimated mass lies in the 15--20 MJup range. These findings validate the reliability of our multi-wavelength photometric-selection methodology. Conclusions. These results offer valuable insights into the low-mass end of the initial mass function and demonstrate the effectiveness of Euclid in identifying brown-dwarf and planetary-mass candidates in nearby, densely packed star-forming regions.