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What do we have here. LXQT + IceWM ( Trisquel Theme ) + Picom. At the moment I am only with Qt applications I don't expect a very well integration with GTK3 apps, I will see.
After some research for alternatives the only one that I found quite close to Dolphin is Pcmanfm-qt. If each of the software is visually correct ( even if I had to fix icons issue on PcManfm-qt ) it is quite different when it comes to use and configure Pcmanfm-qt which is still being very far from Dolphin. ( Also note the issue in the arrangement of the folders in pcmanfm-qt ). A little bug however with Dolphin where 'minimize' and 'Maximize' are not available.
PCMANFM-QT

DOLPHIN

I am far from being convinced by pcmanfm-qt and for now Dolphin wins the match.
Others remark like the connection via the network to an ftp server, which does not work on pcmanfm-qt and the inability to change the size of the icons on the fly.
Still a lot of work to be done on Pcmanfm-qt and at the speed at which development is going on we should reach a similar level in twenty years :D
Others files manager I have tested.
QTFM

INDEX-FM

I have to admit that has nothing to do with the beautiful screenshots from their website...
Anyway, in any case Dolphin wins the match.
After some research for alternatives the only one that I found quite close to Dolphin is Pcmanfm-qt. If each of the software is visually correct ( even if I had to fix icons issue on PcManfm-qt ) it is quite different when it comes to use and configure Pcmanfm-qt which is still being very far from Dolphin. ( Also note the issue in the arrangement of the folders in pcmanfm-qt ). A little bug however with Dolphin where 'minimize' and 'Maximize' are not available.
PCMANFM-QT

DOLPHIN

I am far from being convinced by pcmanfm-qt and for now Dolphin wins the match.
Others remark like the connection via the network to an ftp server, which does not work on pcmanfm-qt and the inability to change the size of the icons on the fly.
Still a lot of work to be done on Pcmanfm-qt and at the speed at which development is going on we should reach a similar level in twenty years :D
Others files manager I have tested.
QTFM

INDEX-FM

I have to admit that has nothing to do with the beautiful screenshots from their website...
Anyway, in any case Dolphin wins the match.