Google’s John Mueller said there is currently no official “mechanism to block indexing of a part of a page.” There are “hacky ways” he said but nothing official from Google like a googleon/googleoff tag that is supported only for the Google Search Appliance, not Google web search (the public search engine).
Of course, he added, you can use new nosnippet controls to hide what content Google shows for your search results snippets. But you cannot stop Google from indexing a portion or part of your page.
Here is John’s tweet:
It has no effect in websearch. There’s no mechanism to block indexing of a part of a page (other than hacky workarounds). You can use data-nosnippet to block a part of a snippet though.
— ? John ? (@JohnMu) March 3, 2020
What would be a hacky way? Hiding content in weird JS based image loaded something. Find something that Google cannot crawl…
Forum discussion at Twitter.