You were correct (thank you so much!). Apparently I set the Update VM to "none" in the Global Settings, so it didn't work. Now installing Whonix works fine.
However, uninstalling the old templates still does not work. The dom0 terminal only replies with "No match for argument: qubes-template-whonix-gw" and "Error: No packages marked for removal". Although I assume as I am already starting to reinstall Whonix, the old templates won't matter as much. -- You received this message because you are subscribed to the Google Groups "qubes-users" group. To unsubscribe from this group and stop receiving emails from it, send an email to qubes-users+unsubscr...@googlegroups.com. To post to this group, send email to qubes-users@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/qubes-users/5d67d016-212b-4477-8207-32f39f463313%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.