The second part of the keyword, "plugins pack 2021," refers to a collection of extensions (also called plugins) that were popular, useful, or newly relevant around the year 2021. These "packs" are typically unofficial compilations curated by third-party websites or enthusiast forums, offering a bundle of .rbz extension files designed to be installed together. Unlike official software downloads, these packs are not produced or endorsed by Trimble, the company behind SketchUp.
Note: For older .rb script files occasionally found in older legacy packs, you may need to manually copy and paste the files into the SketchUp 2018 ShippedExtensions folder located in your system's AppData directory. Managing Plugin Conflicts and Performance full sketchup pro 2018 v18016975 plugins pack 2021