Sorry ahead of time that it's kinda long post. I had a few ideas in this mockup,
so I'm gonna try to group them as best as I can.

https://image.ibb.co/dVjHK7/Dolphinbreeze.png

Location bar
Location bar in the tool bar. Nothing new here but it is visually more
appealing then current and helps to make dolphin look more modern.

Places
Recent Documents should replace recently saved. It's easier to navigate than
recently saved and usually you only want one of the last documents you
touched.

Mounted devices should have an eject button on them on hover.

Remote
Should have a entry to clearly add shared folders instead of an ambiguous
network folder.

KDEconnect devices should also appear here instead of devices as they are
wirelessly networked devices.

https://image.ibb.co/ebq5p7/Dolphin_Tabs.png

Tabs
Tabs should have more padding on them. Currently they vary drastically in
size based on the current folder name and it just looks unfinished. They should
be on top like modern web browsers to keep the metaphor familiar and make
it more readable when using split views.

Panels
When view nearest to the panel size is constrained it should fold away and
leave a FAB with its icon on it. If there is multiple panels then then we could
prolly use the vertical show more button "|||" to show all panels.

For usability Panels should stay open when a new split view is opened until
the user clicks somewhere so they have time to navigate to a new folder without
having to click the FAB.

Status Bar
When losing focus the Status bar text should also become inactive this helps
a lot with split view accessibility.

Shadows
The standard FAB shadows are too big they look like they're their own window
or something so I lowered them. I also added a drop shadow on the toolbar to
help separate the folder view from panels.

Edited for wrong image.

I don't know about the top shadow but I love the rest. Good ideas.

al-dy wrote:I don't know about the top shadow but I love the rest. Good ideas.

I figured otherwise it otherwise make places indistinguishable from the folder view.

https://ibb.co/dm1xOn

This is without the shadow.

A couple of thoughts:
Perhaps put a shadow between the file view and the panel(s) (as well as between the file view and the path bar). This would suggest that the file view is under the other elements.

Perhaps hide or use a lighter shadow when the file view is scrolled to the top to add another visual cue when you can't go up any more (and add a similarly-behaving shadow to the bottom).

(I could see having the scroll-shadow effect built into the breeze theme so that other uses of the scrollable view area could benefit)