Post-Pandemic Trends of 24-Hour Movement Behaviours and Mental Health Outcomes in Youth

Background/Objectives: The COVID-19 pandemic disrupted youth movement behaviours and mental health, but evidence on post-pandemic trends remains limited. Therefore, this study examined differences in compliance with the 24-hour movement behaviour guidelines and their association with mental health outcomes among Portuguese children and adolescents between 2022 and 2024. Methods: This repeated cross-sectional study included two independent samples of Portuguese children and adolescents from the 2022 and 2024 waves of the Health Behaviour in School-aged Children study (2022: n = 2775; 2024: n = 2381). The 24-hour movement behaviours (physical activity, sleep and screen time) and mental health outcomes, assessed by Depression Anxiety Stress Scales—21 (DASS-21), were self-reported. Prevalences of attaining the 24-hour movement guidelines and DASS-21 categories were calculated and compared between 2022 and 2024 using chi-square tests. Adjusted logistic regression models were used to examine the associations between movement behaviour compliance and mental health outcomes. Results: From 2022 to 2024, the proportion meeting physical activity (7.5% to 13.7%; p < 0.001) and screen-time (12.8% to 28.2%; p < 0.001) guidelines increased, while adherence to sleep recommendations did not differ significantly (42.4% to 41.2%; p = 0.365). The proportion meeting two or more guidelines was also higher in 2024 (9.5% to 20.1%; p < 0.001). The prevalence of mild-to-extremely severe symptoms was lower in 2024 than in 2022 for depression (34.2% to 43.9%; p < 0.001), anxiety (38.1% to 43.2%; p = 0.001) and stress (23.6% to 31.0%; p < 0.001). Meeting screen-time and sleep guidelines was associated with at least 31% lower odds of having depressive, anxiety and stress symptoms (p < 0.001). Conclusions: More favourable prevalence estimates for movement behaviours and mental health outcomes were observed in 2024 than in 2022. Compliance with screen-time and sleep guidelines was associated with lower odds of depressive, anxiety and stress symptoms.