really frustrated, I keep failing tests, I know C++ I have 7 years dev experience with it on Windows, granted there are some really advanced tricky things I do not know. Anyone else having a similar issue? How can I resolve it?
The title of your post says that you're taking tests about C++. It seems more likely that something different is being tested.
For instance, if the tests require you to quickly work through algorithmic problems, knowledge of C++ isn't sufficient. Start by figuring out what you need to study.
Ive coded in c++ since the late 80s (c with cout style admittedly) and daily find details I did not know, partly due to missing '11 and '17 updates (11 we didn't buy a new compiler soon enough and 17 I was out of the language for a few years).
If its some nitwit asking obscure language gotcha details and closed book / no web, then you need to install a photographic memory. If its a reasonable test or open book etc, focus on the bigger picture and look up details when you need them.
windows programming has a lot of things outside standard c++, including the xor dialect (managed?). Your experience could be as much trouble as benefit, depending.