SUMMARY
KDevelop has source formatting profiles for the most common programming languages, but lacks support for a (simplified) profile for the other kind of files one can encounter in source trees.

STEPS TO REPRODUCE
1. Load a project like Otter-Browser into KDevelop (github:OtterBrowser/otter-browser)
2. open the toplevel CMakeLists.txt file
3. add a line to it or change indentation of existing code

OBSERVED RESULT
Typically KDevelop will be configured to use spaces for indentation, and this will then be used in the file you are editing. The cited project uses tabs. You can configure the editor to use tabs for the C++ files in *just* this project but not for the CMake files (which are sources!) nor for any
other type of text file in that project.

EXPECTED RESULT
Tabs should be used, as customisable via a category in the Source Formatting options to configure the formatting options that make sense for any kind of text file.
I'm aware that there are transient ways to set the indentation options but those are available only via the status bar and need to be reset each time. The alternative of adding a Kate modeline isn't always acceptable.