The laptop apparently is taking up ~87 gigabytes of space for system. I don't know how to dig into the details of why and to look into possibly freeing up some of that space as that seems rather excessive. I asked a friend and they only had ~11gb associated with system.
I did have a hard time upgrading from high sierra to mojave, and had to do a reboot into safe mode then hit some buttons on the app store to install mojave which eventually seemed to work.