The most common (though not only possible) cause of crash on quit is a misbehaving extension. Individual extension authors, not the Trimble team, are responsible for fixing bugs and/or incompatibilities in extensions. Have you checked that all your extensions are updated to the latest versions? Was there an extension that you added about a year ago?
I assume your truncated final sentence was going to say “We do not get a BugSplat”? There are some sorts of crashes that BugSplat cannot catch. But they still leave a crash report file in
replace “yourid” in the previous with your macOS user id. Note: your Library folder is hidden by default in Finder but you can use Finder menu Go->Go to Folder… to enter that path.
There should be file(s) there with names beginning SketchUp_2018- and extension .crash. If can locate one of those and upload it to this topic, an expert from the Trimble team may be able to diagnose the cause of the crash.