In the Intel® Quartus® Prime Software fitter report for Non-Global High Fan-Out Signals, you can see two columns, Fan-Out, and Physical Fan-Out.
Fan-Out is how many connections there are in the netlist; this will also match the fan-out reported in the Timing Analyzer.
Physical Fan-Out is how many destinations there are in the routing tree.
These will often be the same but can be different for paths going to hard device structures, e.g., an enable signal going to n registers will have a Fan-Out of n, but if the registers are all in the same LAB, then the Physical Fan-Out will be 1.
For example, The netlist for RAM blocks uses separate atoms/nodes for each 1-bit RAM slice. So RAM can be built from multiple atoms, each with its own clock, enable, address, etc., ports.
However, once those atoms are clustered into one physical RAM location, they will have only one physical connection. e.g., despite multiple atoms and ports in the netlist, the clock, enable, etc. signal is only routed once to each physical RAM block.