In general: have you read the evaluation guide: https://www.mendix.com/evaluation-guide/
ReactJS: https://www.mendix.com/evaluation-guide/app-capabilities/front-end
Regarding the ADA/AREA Compliance: https://ww2.mendix.com/rs/729-ZYH-434/images/Building%20Apps%20for%20Accessibility%20and%20Inclusive%20Design.pdf
Mendix & Microservices: https://www.google.com/search?q=mendix+micro+services