From the manual (always check the manual first)

passed_ss is TRUE if the taxon passed the sensitivity analysis, i.e., adding different pseudo-counts to 0s would not change the results

The sensitivity analysis is explained in the ANCOM-BC2 tutorial

Sensitivity analysis for the pseudo-count addition: Like other differential abundance analysis methods, ANCOM-BC2 applies a log transformation to the observed counts. However, the presence of zero counts poses a challenge, and researchers often consider adding a pseudo-count before the log transformation. However, it has been shown that the choice of pseudo-count can impact the results and lead to an inflated false positive rate (Costea et al. 2014; Paulson, Bravo, and Pop 2014). To address this issue, we conduct a sensitivity analysis to assess the impact of different pseudo-counts on zero counts for each taxon. This analysis involves adding a series of pseudo-counts (ranging from 0.01 to 0.5 in increments of 0.01) to the zero counts of each taxon. Linear regression models are then performed on the bias-corrected log abundance table using the different pseudo-counts. The sensitivity score for each taxon is calculated as the proportion of times that the p-value exceeds the specified significance level (alpha). If all p-values consistently show significance or nonsignificance across different pseudo-counts and are consistent with the results obtained without adding pseudo-counts to zero counts (using the complete data), then the taxon is considered not sensitive to the pseudo-count addition.