go to packages.json then, add this "--openssl-legacy-provider" to the scripts
BEFORE (ANTES DE EDITAR)
"scripts": {
"start": "react-scripts start",
"build": "react-scripts build"
}
AFTER (LUEGO DE EDITAR)
"scripts": {
"start": "react-scripts --openssl-legacy-provider start",
"build": "react-scripts --openssl-legacy-provider build"
}