When I open the project, it tells me to rebuild, when I press yes, it gives the error you see in the title
I believe I’ve seen this when making a chance to the code or classes. It wants the project rebuilt through your IDE. Depending on your OS it could be Xcode, Visual Studio, VS Code…
If you go to your project folder there should be a file with the project name and “.code-workspace” extension. Opening this should start your IDE. From there you want to run a Build Task or Build Solution selecting the task that has “Editor” in its name and refers to your OS. In VS Code on Windows 11 I do: Terminal->Run Build Task-> MyProjectEditor Win64 Development Build.