Google's Danny Sullivan has said that using the nosnippet tag won't prevent your pages or passages from your pages from being ranked in Google Search. Danny Sullivan said on Twitter "you can't use it to block parts of a page from being indexed for ranking."
It is not a bad question because you can use the nosnippet tag to prevent your pages from showing up as featured snippets. It is clearly documented over here that you can do that.
But as you know, passage indexing is not about the snippet, it is about ranking. If you don't want Google to rank a page of yours, you can block Google from crawling and ranking the page. But passage indexing is not a featured snippet, it is just another search result in the Google search results. You cannot block that from showing up, without blocking Google from indexing the page.
The nosnippet tags are designed to control how Google shows your search results. We do not even know if the search results for passage indexing will look any different.
Here are Danny Sullivan's tweets:
So, nosnippet is a display option. It doesn't block content from being indexed. And we typically don't have options to prevent just some content on a page from being indexed because cloaking, spam, etc. You can, of course, block an entire page from being indexed.
— Danny Sullivan (@dannysullivan) December 28, 2020
That is the feedback. You can't use it to block parts of a page from being indexed for ranking. And we don't recommend people try to somehow do anything special about passages overall: https://t.co/sVI5d0ak6e
— Danny Sullivan (@dannysullivan) December 28, 2020
And John Mueller from Google chimed in a bit later saying the same thing:
It has nothing to do with ranking, it's purely a snippet control mechanism.
— 🍌 John 🍌 (@JohnMu) December 28, 2020
So why won't the nosnippet tag work? Danny Sullivan said because passage indexing won't make the snippets longer (or maybe different)? So will search result snippets ranked higher because of passage indexing not look any different than normal snippets?
Passage ranking isn't about display. It doesn't cause snippets to somehow get longer. It's about better understanding what a page is about by understanding the context of passages of text, where they can be identified, in *addition* to other ranking factors.
— Danny Sullivan (@dannysullivan) December 29, 2020
So this is yet another difference between featured snippets and passage indexing.
Forum discussion at Twitter.