fixes#5946
Root Cause :
`createDropzone` used a single global `id` for the file input
(`'uppy-dropzone-file-input'`) Clicking any `<Dropzone />` did
`document.getElementById(<global-id>).click()`, which always targeted
the first input in the DOM, so files were added to the first Uppy
instance.
9bac4c8398/packages/%40uppy/components/src/hooks/dropzone.ts (L73-L77)
**Solutions :**
Simplest solution would have been to just make the input id unique per
Uppy instance using `ctx.uppy.getID()`, and click that specific input.
```typescript
const fileInputId = 'uppy-dropzone-file-input-' + ctx.uppy.getID()
```
**Caveats**:
If users don’t pass a custom id to `new Uppy()`, all instances default
to uppy, so ids still collide across instances.
Multiple Dropzones under one instance still share the same id.
Switched to a ref-based approach so clicks trigger the input directly,
without relying on `document.getElementById` lookups. It still falls
back to a DOM click for backward compatibility.
**StackBlitz Link :**
https://stackblitz.com/github/qxprakash/uppy/tree/debug_dropzone/examples/react?file=package.json&embed=1&view=editor&showSidebar=1&hideTerminal=1
**Update: Went for the ID based solution upon discussion with the team
as it's simpler.**
d6b3aa575e