Why can KDevelop syntax-highlighting show codes without suffix?

I’m using KDevelop-5.10 that comes with KDE Plasma-5.27.

I found that KDevelop can show codes syntax highlighting, even through without suffix(*.hpp, *.h), as long as the codes are system headers. e.g:

/usr/include/c++/12/iosfwd

But my headers at /usr/local/include/ can NOT be shown syntax-highlighting, if there’s no suffix(.hpp,.h) with them.

How to let KDevelop show my headers(even without suffix) highlighting? Thanks!