Thanks for sharing your experience! I'm not going to lie, this is all new territory for me. I don't think that I even have an old laptop to install Ubuntu on and, from what I understand, this was necessary as it wouldn't work on Windows? I could always dual boot it on my main Windows laptop, though.
Even with the showhost and ssl_insecure options enabled? I also read the instructions you shared for creating the certificate. I actually saw this a few days ago when I first discovered this thread when trying to learn about mitmproxy! However, I admit that I understood very little of it. Sometimes I feel like I'm biting off more than I can chew!