I made a C++ project with only Release config, because I only need it. When compiling I noticed that there is -O2 flag even it's not set in build options. If you add something else like -O3 they are both included, you don't seem to be able to remove that -O2. Also, related observation is that if you set -s it's not included, but it also doesn't seem to make any difference if you add it in Other compiler options, the .exe doesn't get smaller. I guess this could be just that if you don't use debug information it's same as -s?
The C::B version is 20.03.