That’s actually not hard. Connect the toaster to a smart plug with monitoring, make an automation to send a notification when the power draw drops after X seconds of power draw. It’s essentially the same way people make their washing machines smart.
It relies on xdotool, which I don't think works on Mac?
If I was still on mac, I'd probably try and use hammerspoon somehow. I used that for a few bits of automation, and I know it had ways to choose applications.
Interesting, what do you produce? And how difficult is it?
I heard even Chem students can produce some mainstream drugs sometimes with easy to get products.