Recent developments in spin space groups (SSGs) have led to a new classification of magnetic order and, with it, the emergence of altermagnetism. However, an efficient and routine approach that predicts electronic band topology in magnetic materials by SSGs, and especially the evolution of band topology from negligible spinorbit coupling (SOC) to finite SOC with the symmetry lowering from SSGs to magnetic space groups (MSGs) determined by magnetic-moment directions, has not yet been established. Here, we propose a scheme combining SSG and its MSG subgroups to diagnose band topology in collinear magnets using symmetry indicators of electronic band topology, established for all the 1,421 SSGs and 3,420 MSG subgroups. Specifically, the compatibility relations from SSG to the MSG subgroups can enable a complete topological classification for all possible magnetic-moment directions from the first-principles calculated numbers of occurrences of irreducible (co-)representations at high-symmetry points without SOC with respect to SSG. This scheme can be directly applied to collinear magnets whose magnetic structures have already been determined experimentally or theoretically. Applying it to 488 collinear magnets from MAGNDATA with experimentally determined magnetic structures, we identify 26 materials that are trivial by MSG but are expected to inherit topology protected by SSG symmetry. We showcase Dirac nodal lines and boundary states predicted by SSG but invisible to MSG in FePSe₃. Our work demonstrates the predictive power of the approach combining SSG and MSG over the approaches based on either group alone. The results of high-throughput calculations are expected to extend the magnetic topological materials pool, facilitating future experimental realizations of more magnetic topological materials.