Why does the RTL Viewer shows 'The RTL netlist is not available. Run Analysis and Elaboration to view RTL netlist'?

When choosing the Aggressive Compile Time optimization mode in the Quartus® Prime Pro Edition Software version 19.1 or later, this message may be seen when opening the RTL Viewer after a successful compilation process. When selecting the Aggressive Compile Time optimization mode, the Quartus® Prime Pro Edition Software does not generate a full synthesis netlist to reduce the compilation time. Without a full synthesis netlist, the RTL Viewer cannot elaborate a browsable RTL diagram.

To work around this problem, select a different optimization mode in the Quartus® Prime Pro Edition Software and recompile the design.