How to change the default width for filename

I want the filename width for the default lister to always be 420.
I unclicked "auto-size columns," but it doesn't stay unclicked. Every time I load Opus, autosize is set to autosize, which I dont want.
please advise.

This is covered in your how to customize and save a default layout thread.

The process is the same whether you are turning the auto-size option on or off.