It’s simple. You had extensions installed. Find them and reinstall them.
You can install extensions from within SketchUp, from SketchUp’s Extension Warehouse.
A change from the older SketchUp versions, is that SketchUp now has a dedicated full sized Extension Manager dialog window. (No more tiny Extensions panel stuffed into the Preferences dialog.)
Or, you can download extension archive files (RBZ) and install them manually.
There is a “Install Extension” button on the bottom of the Preferences > Extensions panel (older versions <2017), or bottom of the Extension Manager window (newer versions 2017+.)
There are quite a few. I linked a free one above.
This is a free community plugin that is offered on the SketchUp Team store in the EW …
There have been several of those …
There are also many free extension over at SketchUcation PluginStore.
They have SketchUcation Tools that is a manager that can install plugins and extensions for you.
I seem to remember some unwrap and DXF extensions over there as well.