I am a Linux guy, I prefer to do stuff natively (as opposed to some port to get it to run on Windows), so much less hassle. On my system gcc/g++ and clang/clang++ are part of the distribution, they are updated automatically along with all the other apps. I also have the ability to build the absolute latest (including overnight builds) at any time. For example clang++ 14.0 (not released yet) has reflection, I could build that.
One could consider having the Linux subsystem on windows.
I am attending an OI(Olympiad in Informatics), they compile source files only under GCC 9.3.0, and I work on windows, so I want to find this strange kind of compiler.
But, as TheIdeasMan said before, you probably should grab the latest GCC stable version!
BTW: GCC (MinGW-w64) is not "strange" at all. It's probably the most widely used C/C++ compiler in existence (besides MSVC and Clang). It is a bit strange to require a specific old version though...
I am attending an OI(Olympiad in Informatics), they compile source files only under GCC 9.3.0
Just because they use an older compiler doesn't mean you have to. All that matters is the code written can't have any C++ features from a C++ standard that GCC 9.3.0 doesn't support.