I'm on the mac version, and I open it through the itchio desktop app.
So in fullscreen mode, if I try to alt+tab to something else, the game window disappears and I can't alt+tab to it or see it when I look at all my open apps.
But it's still "open" and when I alt+tab to the invisible app, I still see 7kpp in the top left corner with the dropdown menus on my home bar. If I choose to "hide 7kpp" and then alt+tab to it, the window reappears.
But I assume I should be able to alt+tab between it and other apps without having to do that.