For Chromecast youd still use your account. Since you set it up once, you don’t have to worry about it initially logging into your root account. For iPhone/other apps, yeah that’s what I meant by "not a perfect solution.
I have the same issue as you, but my stipulation is I log in/configure the app, so that way others don’t have my root credentials. There sadly isn’t a “right/good” way around it right now.
I think the issue is that they clearly wrote themselves into a corner with the pseudo 5 year timeskip. They still want the world to feel like the present, but have to deal with the fact that literally nothing would look anything like the present if half the population disappeared for 5 years. It’s hilarious when movies like Spiderman almost completely ignore those events.