You can still use your 2020 license perpetually if you already own it. cannot buy new serial numbers for version 2020.
If you purchased a "Classic" (perpetual) license for SketchUp Pro 2020, your credentials were sent via email. Check Your Inbox: Search for emails from sketchupmail@sketchup.com Sketchup Pro 2020 License Key And Authorization Number
Here is everything you need to know about managing your 2020 license and what to do if you can't find it. 1. Where to Find Your Classic 2020 License Info You can still use your 2020 license perpetually