Click on "Import files" under File in the menu. The window comes up to select the file, but the program seems to have crashed and I am unable to choose a file, move through to navigate in the window, or close the program. I think I used this feature previously, but don't recall what version that was with.
Zettlr Version: 1.8.4
System: linux 5.4.0-58-generic (architecture: x64)