Preview/Simulation not working for iOS

Hello Community,

i am having problems to get Xcode started.

The only thing i want to do right now is simple run a template of (or at least preview) a single view app for iOS.

I work with:

Mac: QuadCore 2,7 GH i5, 8 GB, Catalina 10.15.4, Xcode 11.4

Observation so far: Running the templates of MacOS is possible without problems.

For iOS it is not possible; the preview function does not show up and running/simulating does not work either.

Xcode stucking either at indexing process, buiding process or sometimes even sucessfully builds, but with no preview or further simulation possible. If stuck at indexing, or buiilding process, it keeps running for ever or Xcode crashes. Trying a simulation on a real device (IphoneX, iOS 13.4) doesnt work either.

Even a playground using iOS platform doesnt execute and is running for ever. (Simply selecting MacOS solves this problem though)

Have been trying almost everything that i have found like deinstallation, shutting down processes, clearing caches, clearing device support, clearing derived data, clearing ios support etc., editing schemes, cleaning build folder, setting up new devices, setting up new projects, manipulating of code etc, restarting computer, and even reinstallation of MacOS (with formation of Hardrive), selecting/installing new command line tools,

Further notice: The CoreSimulatorProcess seems to give my computer a hard time. This process slows the computer down. A Playground with an MacOS platform is not possible to run if the CoreSimulatorService has not been shut down before.

Error Message if preview not showing: "Failed to build the scheme"

I really dont understand this (simple) problem. What might be the cause?

Appreciate your help