Modern Macs cannot run unsigned code easily. To install a cracked SketchUp, you often have to disable via Terminal in Recovery Mode.
Check your original purchase email or log into your Trimble account at my.trimble.com – old keys are stored there. sketchup pro license key mac
If you're looking for a free trial or a student/educational discount, SketchUp offers those options as well. You can explore those alternatives on the Trimble website. Modern Macs cannot run unsigned code easily