Supplement Number 1

This supplementary material systematically supports the main text research, covering six parts: S1 demonstrates the bulk state evolution along the kz direction in Mn(Bi₁₋ₓSbₓ)₂Te₄ (x=0.1) through photon-energy-dependent measurements; S2 details the energy gap and Fermi momentum fitting method based on EDC/MDC curves; S3 provides in-situ K doping experimental parameters (deposition time/current); S4 utilizes second-derivative spectra to highlight modulation details of K modification on the band structure; S5 displays the evolution of Fermi surface morphology during K doping; S6 tabulates and quantifies carrier concentrations, Dirac point positions, and non-monotonic changes of topological state gaps with K doses for three samples (MnBi₂Te₄ and Sb-doped systems). Includes 4 references.