How can I make the draggable titlebar file icon always appear at the top of files in Big Sur? I don't know the nomenclature for this, but there used to be always a little file icon at the top of say, a pdf or jpeg which could be dragged to put the file somewhere else (eg paste it into an email).  It looked like this (I'm talking about the little icon to the left of the word 'gray's' in this screenshot):

However, on Big Sur, the default behaviour for this little icon is hidden until I hover my mouse.  So, by default, I see this (sans icon):

I would like this little  icon to always be present at the top of all files, like it used to be.  Is there a way to do this?
(My apologies for not knowing the name for this little icon!)
Backup your plist first. ~/Library/Containers/com.apple.Preview/Data/Library/Preferences/com.apple.Preview.plist
Then run this command:
defaults write com.apple.Preview NSWindowSupportsAutomaticInlineTitle -bool false

It will change the look of the toolbar so the title name is now on its own row above the tool icons. You can revert back to default with this command:
defaults write com.apple.Preview NSWindowSupportsAutomaticInlineTitle -bool true

Alternatively you can change the delay setting from the default 0.5 seconds to 0 seconds with:
defaults write com.apple.Preview NSToolbarTitleViewRolloverDelay 0