Measurements of the thermal Sunyaev-Zel'dovich (tSZ) power spectrum from Planck, ACT, and SPT consistently reveal a lower amplitude than predicted by $\Lambda$CDM models based on primary CMB parameters ($\sigma_8$). This deficit is particularly pronounced at high multipoles ($\ell > 2000$), where the observed power is significantly suppressed compared to expectations from standard gas physics simulations. This "missing power" implies either a lower value of $\sigma_8$ (exacerbating the $S_8$ tension), a significant deficit of hot gas in lower-mass halos, or much stronger AGN feedback ejecting baryons to large radii than currently modeled (Planck Collaboration 2016; Bolliet et al. 2025).