Used yarn eject
Sounds like a duplicate of https://github.com/facebook/create-react-app/issues/10103
This is not an error, your VS Code probably hasn't picked up on the new schema for tsconfig.json as react-jsx and react-jsxdev are newly introduced JSX factories starting with Typescript 4.1 and thus valid values in this context. For me personally VS Code doesn't show any error and even offers them during code completion.
It's resolved in the following way:
Most helpful comment
It's resolved in the following way: