actually the logic of the component selector is NOT what you think.

the idea of the component selector is that the tour will only show in the dropdown when you are in the component

You have actually discovered an important bug. If the banners component is not enabled then ther banners tour should not be enabled either. Not a big deal now but it will be if an extension adds a tour and then you uninstall the extension

Thanks for the clarification, it's clear now.

But I strongly disagree that at the moment it is not so important. There are sites whose admins disable the use of certain extensions (standard for Joomla, we are not even talking about installed ones). In this case, there will be a 404 error.

Agree that this is an issue.
The workaround for now is that you can just disable the tour of an extension if that core extension has been disabled.

I would argue that this is not a bug in the guided tours code - rather its a problem in the tour itself. The banners tour should be constrained by the banner component at which point the problem goes away.

The "general" tours are 'introduction' type tours and perhaps there should be a different mechanism to select, group and present these.

In the case of core tours, when disabling an extension (like banners), the tours should be disabled automatically. When a third party extension installs a tour, the unistall of the third party extension should trigger the removal of the tour. Since the third party installs the tour, it should also take the responsibility to uninstall it.