Why drafts no longer start with blank draft

I preferenser that Drafts app start with a blank page, and is att limited time you have last document open

It use to be so.but suddenly last text.is Always open when startinh drafts

I think you have turned on Focus mode.

Focus mode is the “eye” button on the bottom left of your Drafts.

As @belgarion noted, most likely you have inadvertently turned focus mode on. The other possibility is the New draft after setting has been changed to never or a longer duration:

Hope this helps.