Is there a way to "alt + tab" to last open in Cosmic?

It does, I went and checked. I'll have to continue to question my decision to continue to use Cosmic, I'm doubtful the window switcher for Mutter is compatible.

Action::SwapWindow => {
    let current_output = seat.active_output();
    let mut shell = self.common.shell.write().unwrap();

    let workspace = shell.active_space_mut(&current_output);
    if workspace.get_fullscreen().is_some() {
        return; // TODO, is this what we want? Maybe disengage fullscreen instead?
    }

    let keyboard_handle = seat.get_keyboard().unwrap();
    if let Some(focus) = keyboard_handle.current_focus() {
        if let Some(descriptor) = workspace.node_desc(focus) {
            let grab = SwapWindowGrab::new(seat.clone(), descriptor.clone());
            drop(shell);
            keyboard_handle.set_grab(self, grab, serial);
            let mut shell = self.common.shell.write().unwrap();
            shell.set_overview_mode(
                Some(Trigger::KeyboardSwap(pattern, descriptor)),
                self.common.event_loop_handle.clone(),
            );
        }
    }
}

I can't immediately tell what that is doing, but I don't think it's the last window.

I think it's probably better to just focus on saving the active focussed window history from the compositer. It's definitely known, they highlight the active window. Then, the alt+tab switcher could just use that history. I just have wanted to focus on other things besides trying to submit pull requests for this type of thing. I haven't missed it that bad.

I just took a video earlier of myself switching windows and felt really dumb doing it.