Is this a bug report?

Yes (I think)

However I am just looking for clarification about how to structure projects with CRA. Should I use yarn link instead of symlinks?

Which terms did you search for in User Guide?

"sym" "symlink" "symbolic"

Steps to Reproduce

1. symlink ./src/anything to a directory outside the CRA project directory called anything.
2. Initialise anything with its own package.json that depends on big-integer. big-integer is distributed on NPM with TypeScript files which will be present at anything/node_modules/big-integer/BigInteger.d.ts.
3. Run yarn build and CRA tells me that my project has TypeScript in it and refuses to build.

Expected Behavior

That CRA build wouldn't look in node_modules from symlinked directories.

Unfortunately globby doesn't seem to have an option to ignore symlinks.

Actual Behavior

We detected TypeScript in your project (src/anything/node_modules/big-integer/BigInteger.d.ts) and created a tsconfig.json file for you.

and the build fails because it's not TypeScript