Trimble has indeed killed the free desktop version of SketchUp, replacing it was some cloud-based garbage.
The good news is that you can still download SketchUp 2017 here:
https://help.sketchup.com/en/downloading-older-versions.
Install this. It will allow you to convert downloaded models (in 2017 format) to an earlier version of SketchUp. That is, until Trimble drops SketchUp 2017 format.
It is infuriating that Trimble, who has contributed little themselves to 3DWarehouse, blocks access to the thousands of models lovingly created by others.