You own a "Classic" perpetual license purchased years ago and need to reinstall it.
Some users argue that subsequent subscription versions have offered only marginal improvements, making SketchUp 2021 a perfectly viable tool for many professionals even years after its release. Sketchup Pro 2021 License
A 2021 license is not forever. Eventually, OS updates will break it. You own a "Classic" perpetual license purchased years
Educational institutions have unique licensing options for SketchUp Pro 2021. These typically include: Eventually, OS updates will break it
Historically, users purchased a (perpetual license) for a flat upfront fee. This gave them the right to use that specific version indefinitely. To stay up to date, users paid an annual Maintenance & Support (M&S) fee to receive the next major version release. The November 2020 Shift
Following the change, SketchUp transitioned entirely to a cloud-delivery subscription model. Classic licence reset? - SketchUp Forum
The release occurred during a major transition period. While it was the last version to support the old "Classic" perpetual license, it was also the first version where Trimble pushed heavily toward a subscription-only model. 1. The Classic Perpetual License
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