“We get a nginx timeout.”
This indicates a network connectivity failure.
A log should confirm this with a traceback.
One test is that wkhtmltopdf runs on the command line.
edit: for eg Wkhtmltopdf failing - #4 by pdvyas
You give bench version, but what erpnext and frappe version?
What have you found or tried to debug your case?
Here’s are lengthy threads with what to try