I wouldn’t say most of these are tweaks, given that they’re natively built into Dolphin. This is more of a feature list.

I wish Dolphin was smarter with the split screen. by default, it opens the same directory in both panes on launch, and there’s no way to change that via UI. the last time I checked, you could set it in some config file, so I set one pane to open /home partition, and the other one to open the /stuff partition where I keep all my personal files. it worked great, except that when I’d directly want to open another directory (for example via Firefox’s download menu), it would open in a separate Dolphin tab on both panes, making the entire point of the setup quite useless. it would be nice if I could somehow tell it to open /stuff/Downloads in the pane that usually opens the /stuff partition, while making the root and /home partitions always open in the other one. or even just make any directory open in one of the panes instead of creating a separate tab.