Z:\Games\Microsoft Flight Simulator_1\Content
“Content” folder contains MSFS launcher files, not MSFS packages. You need to find the “Official” folder.
Also, you need to look in the small box at the lower right hand side of the MSFS window, where you will probably see that the target destination for the whole installation is not the same as the actual installation location on your PC.
By clicking on the box, you will be able to navigate to the correct location and the message will disappear.