Both of my bikes are almost entirely built from parts I bought on Taobao, which is the Chinese domestic version of AliExpress. I've bought Shimano stuff (full 105 Di2 groupset, GRX rear derailleur, for example) that's definitely genuine, as well as tires (Schwalbe, Continental, Vittoria, and Michelin) that are also either genuine or good enough fakes that it makes no difference, plus a stack of different brands of Chinese stuff. Most of it has been thoroughly excellent, with no issues whatsoever in thousands of kilometres of riding.