A: Never. The only "permanent free" tools from Autodesk are the Design Review (DWF viewer) and Fusion 360 for Personal Use . Navisworks is a premium enterprise tool.
Includes 4D (time) and 5D (cost) simulation tools to visualize construction sequences and track budget impacts. autodesk navisworks manage 2021 download free
But that doesn't mean you cannot access the software without paying the full retail price. This 2500+ word guide will walk you through: A: Never