Here's a link that describes the process of extracting all indexed pages in Google when it concerns 1000+:

https://www.highposition.com/blog/ho...-your-website/

You can also just do a site: search and browse through the results. That often provides enough clue's of what's indexed in addition to those tag pages.

You could also use a tool like Xenu to scrape every URL of your site, though that doesn't indicate whether it's indexed in Google or not but does give you a complete picture.

The drop in rankings can be caused by an excessive amount of duplicate content and/or thin pages caused by the tag pages.

Google does not penalize a WordPress (or any other) site for having archive pages that publish and point to the same content. They have mentioned this many years back in 2008 itself - Official Google Webmaster Central Blog: Demystifying the "duplicate content penalty" So you don't have to worry excessively about this. Maybe your site will come back in rankings in a couple of days.

However, my advice would be to keep the post’s content to excerpt length when it is published on archive and tag pages. This will also allow easier browsing for your site visitors.

Tag pages are all duplicate internal pages. Most of those pages will be buried in Supplemental SERPs.

I always deindex my blogs tags and keep them deindexed. I suggest to restore the setting back to the way it was and be patient.

[DELETED]

There is no reason to index your tag pages or category pages, undo it.

Don't to the guy citing a blog post by Google 6+ years ago. SEO changes monthly so don't read legacy it and consider it fact.

I would wait a few weeks or so and just see what happens. It may bounce back on its own.

Most likely DUP content issues with all those tag pages. They arent necessary, might as well take them off.

For category pages..

I edit my theme to remove the showing of posts, and use a shortcode plugin to display the posts from that category.

I then use a plugin to enable HTML in category descriptions, and add a bit of code to display that description. What I get is a category page that I turn into a ranking money page.

For example, if my homepage targets "juicer reviews", then my category targets "breville juicer reviews" and contains similar content to the homepage, except that it lists all of the breville juicer reviews.

All of the posts link back to the category page, and I find it works extremely well.

Should be many reason in SERP drop..bad(low quality backlinks) backlink, duplicate content, doing black hat SEO. On pages problem or more.

Check your backlink profile immediately. The algorithm has changed from what it used to be in the past. If you have any irrelevant backlinks in your profile, then remove them through the disvow tool. This will help you in restoring the keyword positions. Before, building new backlinks kow about the latest algorithm so that you know how to build new backlinks.

kindly make Noindex again your TAGs page because this is creating duplicate content in search engines if there is canonical tag is missing. Kindly restore them again.