I'm using an external monitor with my laptop in expanded display mode.
Joplin is having frequent screen tearing issues when I use it with an external monitor (dual monitors).
This phenomenon only occurs when I click on the Joplin system icon from the tray to display the main window. It returns to normal after a while.
Joplin 2.1.8
Win10 Pro 20H2
You can see that there is a tear in the text display on the left side of this image vs. the right side