> The phrase "Chinese Mainland" when used in English comes loaded with the suggestion that Taiwan is rightfully part of China

For better or for worse, many people on both sides of the strait have used language along these lines that suggests that Taiwan is part of China for decades and probably even since a bit before 1949 (I was not alive at the time). I think that, at this point, the term “mainland China” is just the default.

That being said, a person from China could just say they’re from China and no one would be confused. This is in contrast to someone saying they’re Chinese, which can be ambiguous.