Typescript не ругается, но при передаче его через пропсы ругается что нужно всё типизировать как string | string[]:
const projectInfo: (string | string[])[][] = [['Registration form', 'Page with registration form of four fields, which displays an error notification if it is incorrectly filled.', ['Javascript', 'CSS']], ['Giphy', 'Page for search and watch gif files, from Giphy API. Multiple language and may copy gif.', ['React', 'Redax', 'Axios', 'CSS']], ['Landing Glopt', 'A page with several section, addaptation for any device.', ['Javascript', 'SASS', 'GULP']], ['Project Euler', 'Answers and solutions to problems of the famous Euler project.', ['Javascript']]
];