It doesn’t appear that the subtract mode and the extract mask function work right now.

We get a lot of reports about this, so your feedback is valid. Unfortunately I’m repeatedly stumped because with each comment I re-test the addon with the latest version of Blender and it still works for me:

Granted, the tool has always been finicky. It’s not uncommon for me to repeat a certain cut several times from slightly modified angles and/or slightly modified strokes until it works as desired. It’s a free tool without an active developer, meaning finickiness comes with the territory.