  Spin chains proximitized with superconducting condensates have emerged as one
of the most promising platforms for the realization of Majorana modes. Here, we
craft diluted spin chains atom-by-atom following seminal theoretical proposal
suggesting indirect coupling mechanisms as a viable route to trigger
topological superconductivity. Starting from single adatoms hosting deep Shiba
states, we use the highly anisotropic Fermi surface of the substrate to create
spin chains characterized by different magnetic configurations along distinct
crystallographic directions. By scrutinizing a large set of parameters we
reveal the ubiquitous emergence of boundary modes. Although mimicking
signatures of Majorana modes, the end modes are identified as topologically
trivial Shiba states. Our work demonstrates that zero-energy modes in spin
chains proximitized to superconductors are not necessarily a link to Majorana
modes while simultaneously identifying new experimental platforms, driving
mechanisms, and test protocols for the determination of topologically
non-trivial superconducting phases.
