With the Apple update to Big Sur 11.2, Sketchup Pro has disappeared from the tool bar and from the applications folder.
Any chance you’re logged in as a different user? macOS updated certainly do not uninstall software. Try a Spotlight search (magnifying glass in upper right of screen) and type “SketchUp” to see what shows up.
I believe it is actually a good thing, by the looks of the application folder, the install on your prior OS was probably not done as it should have been.
Better download the installer .dmg file at www.sketchup.com/download/all and start it up.
When a panel with two icons appears, drag the icon of SketchUp into that of the Applications folder.
Where is you SketchUp 2021 folder located? It should be in the Applications folder, but it’s not there anymore. It’s looking for it in the Applications folder, that’s why it can’t find it.
I deleted all traces including empty icons and re-installed the whole thing. Hopefully it will stick around for some time as it had in the past. I have no idea why it departed after the OS update.
Thanks all for your support.