Ensure to copy your n8n workflow and paste it in the code block, that is in between the pairs of triple backticks, which also could be achieved by clicking </> (preformatted text) in the editor and pasting in your workflow.
```
<your workflow>
```
That implies to any JSON output you would like to share with us.
Make sure that you have removed any sensitive information from your workflow and include dummy or pinned data with it!
I had no problem sending email with an attachment. Does your Google Drive node immediately preceds the SMTP Email node? If not that might be the reason. One way or the other, the binary file has to end up in the node that immediately preceds the node where that file is required. To achieve that you can apply one of the techniques described in [onedrive via Graph HTTP] why binary don't upload if not exactly previous node? - #2 by ihortom
Yes, thank you very much for your response. Indeed, the problem was that I had put Google Drive in a Third-Party Application on my n8n path.
(See picture)