I recently installed 25.03 with MinGW, and set MinGW as the default compiler.
I then installed TDM64-GCC 10.3.0-2 to check some things about the Code::Blocks MinGW against TDM.
When I when back to the Code::Blocks MinGW in the Compiler settings, I noticed the Compiler flags box is empty.
I uninstalled TDM, but the Code::Blocks MinGW compiler flags box is still empty.
That's happen from time to time. I don't know the reason. Try to click on Reset Default, eventually change the compiler and come back to the default one. May be also, close and reopen C::B. Normally, thats solve this problem.