This study is a Phase Ib, multicenter randomized, double-blind, dose-escalation, placebo-controlled trial designed to evaluate the safety, tolerability, PK, and PD profiles of multiple-dose ACT500 in participants with metabolic dysfunction-associated steatotic liver disease (MASLD) complicated with chronic hepatitis B (CHB). The trial plans to enroll 24 participants with MASLD complicated with CHB across three dose cohorts initially, each consisting of 8 participants who will receive oral ACT500 tablets once daily.