That option is either not explained well, or not what OP was really asking for. It doesn't specify what's the default behaviour for extensions that are neither explicitly enabled, nor disabled. It also doesn't say how to disable everything apart from some set of extensions.
Extensions to me mean something that I explicitly choose to install (regardless of whether they automatically update). As far as I can tell, Zed goes about downloading code (“extensions”?) invisibly with no user input. See, for example, https://github.com/zed-industries/zed/issues/12589
> or you have an "official" extension manager that rolls out an update every next year