Improve UX for "Open" toolbar button
At least since Libadwaita, apps come with a new and improved "open recent" popup, that lets you search through your recent files and delete them from the list. Instead of just replacing the old drop-down list for recent files that was reachable clicking on the arrow next to the "open" button, the "open" button was unified to only offer one action, being the "open recent" dialog. Opening other files than the recent ones now requires clicking a button inside the "open recent" dialog.
Being a big fan of the improved popup, I still want to point out how its current implementation negatively impacts UX and propose a solution.
UX impacts of the current implementation
For new users
New users are probably going to take a while figuring out how to get from the "open recent" popup to the actual "open" dialog, as the button is not very prominent and not labelled.
No matter which way they are going to use the application, they have to learn about the actual "open" dialog along with its folder structure anyway, as the "open recent" popup is going to be useless at the first application start. This means that they have to learn one user interface more in order to achieve basic usage of the app than if the "open" button directly triggered the "open" dialog.
For power users
"Power users", or people who spend more time on their computers searching for ways to make their workflow more efficient, are probably the main beneficiaries of the improved "open recent" popup. For them, this is a welcome shortcut to open a file they know they've opened recently without navigating through their folder structure.
For them, however, the new unified "open" button also declines user experience in the case they want to open a file they haven't opened recently. In these cases, they have to perform an extra button click. The actual "open" button inside the "open recent" popup is not very accessible or ergonomic, as it is very small and still quite far away from the unified "open" button in the toolbar. According to Fitts's_law, this is unfavourable (and I've experienced it as unfavourable myself).
Proposal
I propose splitting the "open" button again into the "open" part that triggers the "open" dialog and the "arrow down" part that triggers the new and improved "open recent" popup. This improved the UX in the first use case without significantly impairing UX of the second use case.
The small "open" button could be removed from the "open recent" popup.
In case no recent files are available, the "arrow" wouldn't even be shown and only the "open" button remained as a single, regular button. This avoids confusion, clutter and unnecessary clicks to a menu that you can't use anyway (however, the "empty" state of the popup would still be important in case of triggering it using the ctrl + k shortcut).
New users are going to directly be taken to the "open" dialog they are going to have to use anyway, without being imposed on an additional layer of UI they have to learn because the actual "open" button is nested inside this kind of extra menu.