Noctalia is a desktop shell for window managers. Tiling and scrolling window managers (such as i3, MangoWM, Niri, etc.) are only window managers. They don’t have any kind of graphical way to launch applications, there’s no dock, bars or widgets of any kind. They only manage the windows, and you need to provide the rest by installing a number of different applications. Noctalia is a shell that provides a full desktop experience with all the bells and whistles you might expect from full desktop environments like KDE and Gnome.
The previous versions of Noctalia were based on Quickshell which was a memory hog. It used few hundred megabytes of memory per each display you had. Noctalia v5 is a complete rewrite in C++, which especially on multi-monitor systems uses only a fraction of the memory usage compared to Noctalia v4.
I switched from KDE to Niri+Noctalia a few months ago. It’s highly customizable and pleasing looking environment. There are templates for different applications which applies your chosen color theme to applications so that you have unified look across all (or most) of your applications.
I use it with niri on debian stable. Works pretty good, no Talia is awesome, but it’s no replacement for a full desktop. One thing that bothers me for example is that the no Talia calendar isn’t actually showing my own calenders events. I didn’t find a way to configure it.
The shell itself is very impressive and probably the best thing if you don’t use a DE.
So, I came from Gnome to Niri + Noctalia, and one or the other of the latter read from Gnome’s settings. My calendar stuff works great, but that’s because I set everything up in Gnome first before later migrating.
I also had an issue with Pipewire video streaming not working on Niri one day (streaming to the internet, not from), and opening Gnome to see if that worked reestablished some xdg-portal config that had gotten lost somehow.
And so I keep Gnome for fear of losing those QoL things in Niri. I dunno if I’d recommend installing it just for that, but maybe that will give you some clues on how to solve your issue!