The install of Linux 18.1 was clean install- not an upgrade- also a reboot will bring everything back to normal-
Sheesh, everything’s going trans these days!
Are you anywhere near full disk capacity on the machine?
I’ve seen behavior like that when I am near capacity on the system.
You could also pick a different Linux distribution. The leader of Linux Mint, Clement Lefebvre, said in 2009, that he doesn’t want your money if you support Israel. I’d oblige. If you do keep Mint, you can avoid sending him money by not using the default search engine, or default music downloader. I’m not sure what other ways of using Linux Mint send money to it.
Here are 2 links about his statements in 2009:
https://www.extremetech.com/computing/83296-the-great-linux-mint-political-train-wreck
http://abriefhistory.org/?p=774
It sounds like a video driver problem. I have Cinnamon on one of my laptops and has never given me problems except that it doesn’t like to “wake up” after being asleep.
One thing you could check is how you have your nemo (default) file manager set to display items. I find that by setting options for display other than default can cause my desktop to become quirky.
The desktop display is only a glorified folder after all.
If you haven’t tried these - there are 2 post install steps you should do. One - run updates...make sure you have a green check mark in the lower right notification area. If its a blue exclamation point - click it, enter your system password - and let it run. That initial batch of updates solves a lot of problems - especially boot issues.
If you continue to have problems - check to see if there are any proprietary video drivers available for your video card. I think there is a menu link under “Administration” called “Drivers”. Click it - and it will tell you if there is a driver available...I’m generally pretty happy with the stock generic video driver - pretty solid these days.