As someone who doesn't regularly use KDE, can you tell me how you set the scaling for your display? I just want to make sure I am replicating your setup.
To address the original question - we got rid of dpi_scale since we are on GTK3 now and should be properly grabbing the scale from GTK.
That said, GTK has integer scale amounts in addition to text scaling. I am looking into KDE to see how we can properly detect this and not require users to use ui_scale.