brew install openssl
openssl req -x509 -newkey rsa:4096 -keyout cert.key -out cert.crt -sha256 -days 3650 -nodes -subj "/C=XX/ST=YOUR_STATE/L=YOUR_LOCATION/O=YOUR_COMPANY/OU=YOUR_ORG/CN=YOUR_DOMAIN"
Replace the values with yours
Now modify the run script to
HTTPS=true SSL_CRT_FILE=cert.crt SSL_KEY_FILE=cert.key react-scripts start