Garage exposed NM wiring - protection?
Voltage application of 8’ is considered protected by elevation.
infact live parts can be considered protected above 8’ 50-300v.
8’7” is good for 1000v these are live parts see NEC 110.27.
Beyond that ask the inspector to cite the code reference.
There is no code reference that states all horizontal runs require protection.
Look at the code for a crawl space or a basement attic both are horizontal runs that usually are below 8’ and permitted on surface runs per NEC 334.15.
The exact height for protection from physical damage is not listed and I have provided multiple examples where protection by elevation is allowed and exposed nmb is allowed below the height you have.