At some point SketchUp upset macOS, and was put into quarantine. That can happen if you run SketchUp from an unconventional location. For example, running it from the disk image instead of from the Applications folder.
We did do something to try to make it less likely to have a problem, even when run from the wrong location. It looks like you’re not running the latest version of 2021, you could try updating, and see if the later one behaves better.
Here’s the disk image:
https://www.sketchup.com/sketchup/2021/SketchUpPro-dmg
Open that disk image, and drag the SketchUp 2021 folder on to the Applications alias, and let it replace the version that may already be there. After it is copied, eject the disk image, then go into Applications/SketchUp 2021, to run SketchUp.
It may be that macOS is still not happy, you might as well do the steps needed to make it be happy, before installing the update. Look at the steps I gave in this post: