Disabling extension warehouse on older versions

You can download extensions from the extension warehouse website as well as 3D models from the 3D warehouse website, you can also download the sketchucation store plugin from the sketchucation website install it and download extensions from that store, if you want to use fredo plug-ins you must have installed the latest version of the sketchucation store by the way.
To install a plugin you must go to extension manager and on the bottom left corner you’ll see a button that says install extension, click on it, search the rbz file you downloaded open it and it’s done.
Here are links to the websites.

https://extensions.sketchup.com/