Thinclient is gotten by disable classic mode in preferences under 'interface', so if that option not unticked on your end, then you're not using thinclient mode.
Yes that is the one.
So it doesn't have the last option shown, on the pic listed on github project page here?
https://github.com/cas--/autoshutdown
You shouldn't need anything to make that option show - I saw it myself in quick test previously today before replying to you.
Yes, add it again is fine, just remember if using thinclient, then should be both places in v1.5, unless using thinclient on same machine so only one profile dir. Stop/start deluge also if didn't before and enable/disable plugin again.