We present a photometric and spectroscopic analysis of the Type Ibn supernova (SN) 2024acyl. It rises to an absolute magnitude peak of M_o=-17.58+/-0.15mag in 10.6 days, and displays a rapid linear post-peak light-curve decline in all bands (e.g., gamma_0-60(V)=0.097+/-0.002mag/d), similar to most SNe Ibn. The optical pseudobolometric light curve peaks at (3.5+/-0.8)x10^42^erg/s, with a total radiated energy of (5.0+/-0.4)x10^48^erg. The spectra are dominated by a blue continuum at early stages, with narrow P-Cygni HeI lines and flash-ionisation emission lines of CIII, NIII, and HeII. The P-Cygni HeI features gradually evolve and become emission-dominated in late-time spectra. The H-alpha line is detected throughout the entire spectral evolution, which indicates that the circumstellar material (CSM) is helium-rich with some residual amount of hydrogen. Our multiband light-curve modelling yields estimates of the ejecta mass of M_ej=0.49^+0.11^-0.09_M{sun}, with a kinetic energy of E_k=0.06^+0.01^-0.01_x10^51^erg, and a ^56^Ni mass of M_Ni=0.018M_{sun}. The inferred CSM properties are characterised by a mass of M_CSM= 0.51 (+0.05/-0.04) M_sun, an inner radius of R_0_=17.8^+3.6^-3.0_AU, and a density rho_CSM=(8.3^+2.7^-1.2)x10^-12^g/cm^3^. The multi-epoch spectra are well reproduced by the CMFGEN/he4p0 model, corresponding to a He-ZAMS mass of 4M_{sun} (H-ZAMS mass 18.11M{sun}, pre-SN mass 3.16M{sun}_). These findings are consistent with a scenario of an SN powered by ejecta-CSM interaction, originating from a low-mass helium star that evolved within an interacting binary system where the CSM with some residual hydrogen may originate from the mass-transfer process. We also discuss an extreme scenario involving the possible merger of a helium white dwarf. In addition, a channel of core-collapse (CC) explosion of a late-type Wolf-Rayet (WR) star with hydrogen (WNH), or a transitional star between an Of and a WR type (e.g., an Ofpe/WN9 star) with fallback accretion, cannot be entirely ruled out.