error An unexpected error occurred:
error An unexpected error occurred: "https://registry.yarnpkg.com/react-is/-/react-is-16.12.0.tgz: connect ETIMEDOUT 104.16.19.35:443".
info If you think this is a bug, please open a bug report with the information provided in "C:\\Users\\zhangweixin\\Desktop\\repair-project\\my-app\\yarn-error.log".
info Visit https://yarnpkg.com/en/docs/cli/add for documentation about this command.
info There appears to be trouble with your network connection. Retrying...
info There appears to be trouble with your network connection. Retrying...
Aborting installation.
yarnpkg add --exact react react-dom react-scripts cra-template --cwd C:\Users\zhangweixin\Desktop\repair-project\my-app has failed.
解決方案，參考其他方案刪除yarn文件夾的思路
c盤全局搜索yarn 發現
C:\Users\zhangweixin\AppData\Roaming\npm\node_modules\yarn 刪除 yarn 文件夾即可
當然我也刪除了
C:\Users\zhangweixin\AppData\Roaming\npm-cache\yarn （可能不是這個影響）