next build passes on your laptop. The same commit fails on Vercel with Module not found: Can't resolve './components/Button' or similar, pointing at an import that obviously exists. Nothing in the code changed between the two builds.

Vercel builds on Linux, where Button.tsx and button.tsx are two different files. macOS disks are case-insensitive by default, so on a Mac an import of ./button happily finds Button.tsx. We reproduced the Linux side directly: a file named button.js imported as ./Button.js fails in Node with ERR_MODULE_NOT_FOUND. The Mac side is what hides it from you: per git's documentation, git init and git clone set core.ignoreCase to true on a case-insensitive disk, and then a rename that only changes case is not seen as a change. So you rename the file, the import works locally, git status is clean, and the old name is what gets pushed.

git ls-files shows the names git will deploy, which is what Vercel sees, regardless of what your disk shows. Compare the casing there with the casing in the failing import.

# What git will actually deploy, matched without regard to case:
git ls-files | grep -i "components/button"

# components/Button.tsx   <- committed name
# but your code says: import { Button } from "@/components/button"

Rename through git so the index changes, then commit. In our reproduction the index still held components/Button.js after the file on disk had been renamed, until the rename went through git. Pick one convention (all lower case file names is the easiest to keep) so it does not come back.

# Rename in git itself, not only on disk:
git mv components/Button.tsx components/button.tsx
git commit -m "Fix filename case for Linux builds"

# If git refuses on a case-insensitive disk, go through a temporary name:
git mv components/Button.tsx components/button.tmp.tsx
git mv components/button.tmp.tsx components/button.tsx

If the casing matches: a path alias such as @/ that is set in tsconfig.json but not resolved the same way in the build, a file that is generated by a script your local build runs but Vercel does not (prebuild steps are a common one), or a file that exists locally but is listed in .gitignore. git ls-files settles the last two as well: if the file is not in its output, Vercel never received it.