Siril dark theme not working in Ubuntu 22.04

Hello, I’ve been using Siril on a Windows laptop and recently I built a new desktop running Ubuntu 22.04.

I installed 1.2.0 beta2 initially and noticed a strange behavior. I still had the default Ubuntu appearance settings and when I launched Siril everything seemed fine.

after a while, I noticed that Siril was only coming up in light theme, and I did not change any of the user preferences. Upon experimentation, I found that the Siril dark theme only works when I use the default Ubuntu “Appearance / Style” settings of the orange highlights and light theme. Any changes on the Ubuntu settings have an immediate effect on the Siril appearance

I recently updated via flatpak to the rc1 version and the same behavior exists

This is because the theme you use does not support dark theme.
Try gedit for example. It will behave the same.