I run Linux Mint on multiple computers at home. Recently I reinstalled Linux Mint and was having this strange issue where windows disappeared when I minimized them. They were no where on the taskbar and I couldn’t remember the keyboard shortcut to switch between running applications. After a little digging I realized that “Window List” was not active on my taskbar. Not sure how that happened, but easy enough to fix.
To fix the issue right-click on the taskbar, choose “Add to Panel…” and then add “Windows List”. Easy!