Positive feedback with constant transfer functions
The system you are looking at can't be realized because it has no delay.

Such a system is known as an algebraic loop. Simulink detecs such loops and treats it like an equation and solves for a valid output.

See: https://de.mathworks.com/help/simulink/ug/algebraic-loops.html

Just because Simulink can work with it does not mean that it can be realized or has a physical interpretation.