This article investigates the covert communication performance in STAR-RIS-assisted non-orthogonal multiple access (NOMA) systems, considering the practical scenario where successive interference cancellation (SIC) is imperfect. The authors derive closed-form expressions for the detection error probability (DEP), optimal judgment threshold, average minimum detection error probability (AMDEP), and outage probability (OP). An optimization problem is proposed to maximize the effective covert rate (ECR). Simulation results show that varying the proportions of transmission and reflection components in the STAR-RIS can enhance the ECR. The study also analyzes the impact of the number of STAR-RIS elements on covertness performance. The main contributions include analytical expressions for DEP, an optimization problem for ECR maximization, and a detailed analysis of the effect of STAR-RIS elements on covertness.This article investigates the covert communication performance in STAR-RIS-assisted non-orthogonal multiple access (NOMA) systems, considering the practical scenario where successive interference cancellation (SIC) is imperfect. The authors derive closed-form expressions for the detection error probability (DEP), optimal judgment threshold, average minimum detection error probability (AMDEP), and outage probability (OP). An optimization problem is proposed to maximize the effective covert rate (ECR). Simulation results show that varying the proportions of transmission and reflection components in the STAR-RIS can enhance the ECR. The study also analyzes the impact of the number of STAR-RIS elements on covertness performance. The main contributions include analytical expressions for DEP, an optimization problem for ECR maximization, and a detailed analysis of the effect of STAR-RIS elements on covertness.