Does “Hidden” content, like in the Tabs or Accordion get indexed by Google?

Hidden content will get indexed by Google, but ‘fetched’ content will not.

For example, the Tabs plugin works by either ‘fetching’ content via a portfolio collection or rearrange sections on the page. The fetched content will not be indexed by Google, as this is an asynchronous request. The rearranged content will get indexed by Google.

Don’t take my word for it. You can always check what Google is indexing on a page using the Google Search Console. See more about indexing with this documentation from Google on where to find it.

You can also toggle off SEO in the Page or Collection Settings for it to not be indexed.