Repost the article? Or write a new one?

I had an article that ranked very well before. After the Google algorithm update in October last year, the ranking dropped from the second place on the homepage to the bottom of the Google homepage (9-10th place), and the traffic dropped a lot.

Later, on the basis of the original content, I expanded and added some new websites to this article, and the ranking returned to the top 3 on the homepage after the article update.

In June this year, the ranking of this article has been declining, and now it has dropped to the second or third page of Google. I tried to delete some content of the article, reduce its word count, and add backlinks and internal links to the article, but the ranking of the article still did not change.

In this case, should I rewrite this article based on the original URL? Or rewrite a more in-depth article and redirect the old article 301 to the new article? Which effect is best?

One extra point:
I did a test before, I deleted part of the content in an article and replaced it with high-quality content written by professional writers, but after updating the post, all the keywords of this page were lost and have never recovered. So, is it not recommended to update the content at the old URL, or is it better to publish a new post and redirect the old article 301 to this new article?

Keep the same page URL, there's no point in changing it in your case,
Content-wise, you have to make sure the page has original, readable, non-spammy content that serves the user search intent,

Other than that, it's #1 has something to do with your website/page authority,
The links you're using, especially as the drop is post-update, lost links or website(s) linking to you lost their (or some) of their authority,

Or #2 UX signals are not as good, high bounce rate, short visit times, etc...
If the page doesn't satisfy the users as per Chrome UX tracking, they will drop you down in the SERPs,

The content as textual content on its own is really overrated in SEO,
It's mainly about authority & the UX that has been used for the last couple of years now

Build links to the article

I'd advise going over everything to see if any new/ updated content has come out on your competitor's sites for the articles. Instead of rewriting just either add more content to freshen it up or, do some keyword research and start creating sub-articles linking to the main article which should increase topical authority.

Write new one!

Keep the original URL and inherit the existing link value (including backlinks and internal link weight). If the original content is still valuable to users and the topic has not changed much, it may be more beneficial to update the original article