Warnings only work during development, so this config is ignored in production mode.

[lovetingyuan]

app.config.warnHandler does not work in production mode.
I think Vue should provide an option like "enableWarning" to force print warnings in production.
It is helpful for debugging in production mode, such as using vite preview.

[chenxch]

core/packages/runtime-core/src/warning.ts

Line 34 in 98f1934

if (!__DEV__) return

You can try to clone the core repository, comment out this line of code, and compile a vue yourself. You can use the vue you built yourself, or you can research and patch the official vue.