Hi. I’m using niri with noctalia, cachyos package manager is not applying system theme, while cachyos hello seems to be doing it just fine.
Hello and welcome,
First I might suggest to not use that “package manager”.
Or at least if you must then make sure to do first;
sudo pacman -Syu
But for a real GUI package manager then I would suggest octopi.
As to the issue..
They are different toolkits (GTK vs QT).
So I might guess you have configured one and not the other.
(And/or have not configured any ‘automatically copy style’ type thing.)
Hello @cscs
Yeah, I always update with pacman, I used GUI as more comfortable way to monitor what I have installed, but I’ll give shelly a try instead of octopi just for the sake of keeping new rice look clean 
Judging from the settings though, everything supposed to work, but whatever
Still though it seems that QT is somehow not being applied?
Sorry I do not know noctalia enough to point further than the previous general link.