If SketchUp 2020 is still installed and working on an old computer, go to Help > License > License Info (Windows) or SketchUp > License > License Info The Official License Manager: You can use the SketchUp License Manager
If you can't find your old license or need a newer version, SketchUp now uses a subscription model . Modern versions do use authorization codes. Instead, you simply sign in with a Trimble ID (your email address) to activate the software. Authorizing or Removing a License | SketchUp Help Sketchup Pro 2020 License Key And Authorization Number
If you are writing for an audience looking for these details, here is a structured blog post draft focusing on legitimate recovery and modern alternatives. Finding Your SketchUp Pro 2020 License: A Complete Guide If SketchUp 2020 is still installed and working
Are you trying to move SketchUp Pro 2020 to a new machine or simply trying to get back into your old project files? Finding that "Serial Number" and "Authorization Code" can feel like a scavenger hunt. Authorizing or Removing a License | SketchUp Help
You can still use your 2020 license perpetually if you already own it. cannot buy new serial numbers for version 2020.
Official technical support for the 2020 version has ended as SketchUp now follows a "Current + Previous 2 Versions" support policy. 4. Moving to Subscriptions (Trimble ID)