I am facing the same error : ! LaTeX Error: File `l3backend-pdfmode.def' not found. I have seen some comments mentioning to go to the "Update DB" option in the miktex console. But I am not able to find it. Can anyone help me with a screenshot of how to find this option ? Would be really helpful.
The "Update DataBase" option is a little bit hidden in MiKTeX Console.
- Just open MiKTeX Console
- Choose if you need admin or user mode (depends on your installation). Because I have an admin installation I choosed Admin mode ...
- Click on menu point "Tasks" (near "File", see red circle in the screenshot ...)
- Click on "Update Package Database" to update the database for available packages with MiKTeX (see red arrows in screenshot ...)
- Use this opportunity and click afterwards on "Refresh file name data base" ...
Please see this screenshot:
For the ususal way to update your MiKTeX follow how-do-i-update-my-tex-distribution