Is your feature request related to a problem? Please describe.
I want to embed drag and copy feature in ra data grid. But I cannot access data grid's innerText because DataGrid, DataGridBody does not forward ref to inner material-ui element.

Describe the solution you'd like
Add React.forwardRef to Datagrid.tsx, DatagridBody.tsx, DatagridCell.tsx.

**Describe alternat

hi, after hide columns still show up in columnsButton.

i hide some columns in my table using hidden:true also the show up disabled but still there, have some way to hide columns from there?

and also i have space between index and name columns after hide column

• The issue is present in the latest release.
• I have searched the [issues](https://github.com/mui

In the serverside-pagination example, we have some sample means of adding loading indicators. Loading indicators are a common and important part of the serverside experience, so we should have some better examples here so that other devs can work from good ideas, and we can keep full-fledged loading indicator options out of the core library (E.g. gregnb/mui-datatables#958

Setup Github actions that triggers on PR and runs all unit tests.

IconButton does not 'blur' when it loses focus, retaining it's --background-focused class after the mouse or touch leaves the item.