In Kate, text select colour used to match Global Accent colour in versions prior to 5.24.1. After updating to 5.24.1, the text select colour is the default Blue. I hope this a bug which has been reported or will be fixed in 5.24.2

Which color theme do you use? Kate applies the scheme in use so that might differ depending on your selection. You can always change a color if you don't like it by copying the color scheme, then modify it.