I have same problems - compilar flag tabs are empty (Using standard Codeblock 20.03). It started exactly when I copy default compiler setting (previously updated to gcc 12.1 without any issue) to create copies with different version of gcc (13.1 and 13.2) including renaming default gcc with appendix about gcc version.
I deleted file: options_gcc.xml and it helps restore partially things back. Compiler flags are visible however Codeblocks now report there is no default compiler. I checked the setting, it add "mingw32-" before gcc.exe in C compiler and for linker in dynamic libs. For some versions it include this prefix even before C++ compiler.
I corrected everything and it works.
However noted that I need to do a change on single compiler settings and that "OK" before moving to another one, otherwise it seems it does not change it correctly.