Documentation should include a note that this property will not be visible within Studio’s property pane if StreamingEnabled is not Enabled.
I did unfortunately attempt a code-based solution, because I thought my Studio was bugging/incorrectly displaying information as I was preparing an existing game for a StreamingEnabled conversion before enabling it as the last step.
Page URL: https://create.roblox.com/docs/reference/engine/classes/Model#ModelStreamingMode