If you have any of the following question this post might be helpful.

1. How to override default webpack config of react apps created with create-react-app?
2. How to modify default eslint rules/config of react apps?
3. How to add additional webpack plugins to react apps?
4. How to use custom eslint file when running react apps?

Solution : eject

Run npm run eject or yarn eject.

react-scripts will warn you, simply ignore 😇.

After this process completes CRA (create-react-app) will eject all configs and scripts
There will be 2 new folders in the root of the project

/config ..env.js ..getHttpsConfig.js ..modules.js ..paths.js ..pnpTs.js ..webpack.config.js <----------- webpack config file ..webpackDevServer.config.js ../jest /scripts ..build.js ..start.js ..test.js 

There you go, modify the webpack.config.js files as you wish. Questions 1 and 3 are solved.
For Q2 and 4 you don't have to do anything, once we eject all the configs webpack will automatically use eslint files in the project root.