I have looked around online and noticed a lot of users that moved to Niri come from KDE, or were using Dolphin on their previous WM/DE and want to use it on Niri. The problem is that unlike Nautilus, the Dolphin experience on Niri is not out of the box, it has a lot of issues. 90% of the time you open Dolphin the first time it doesn't work properly and it looks horrible. So I try to write this to stealgather all the fixes that I have found and turn it into a guide for newcomers to make Dolphin functions as close as it was on KDE.
This guide focuses on Vanilla Niri. I personally don't use any plugin or theming shell so I don't know exactly how they work.
At the time I'm writing this I'm thinking of upload it into a gist or something at some point, to make it easier to update things and to access/download. Edit: gist