Operating system: Darwin-18.7.0-x86_64-i386-64bit 64 Bits
Graphics card: AMD Radeon Pro 560X OpenGL Engine ATI Technologies Inc. 4.1 ATI-2.11.20
Broken: version: 2.81 (sub 14), branch: master, commit date: 2019-10-09 22:31, hash: rBf61a8a2abd07
Short description of error
Hair Strand or Strip toggles only shows in Eevee for the viewport. If you only use Cycles you won't even know you have the option to display hair particles by thickness.
If you toggle it with Eevee enabled the settings port to Cycles though.