App styling error: "kf.kirigami: Failed to find a Kirigami platform plugin"

I’m trying to compile my own Kirigami app, but I get what I can only describe as an styling error. You can see what this style looks like with the image below.

This is a screenshot the Kirigami Gallery from the Arch repos.

The thing is that I’m pretty sure I’m using the libraries from kde-builder and compiling Kirigami Gallery works as expected, but that button on the top right corner is not what’s supposed to look like in my app, right? My app’s file picker also uses Fusion instead of Breeze.

There is an error that pops up in the terminal and I think it’s related: kf.kirigami: Failed to find a Kirigami platform plugin. Does anybody know how to fix this?

Edit: I found KAppTemplate, and decided to just build my app from there. I decided to leave this open just in case if somebody leaves something important here.