How to improve the ranking of a top page back to No1?

Ensure an internal page link from the key phrase as anchor text. Also, win 1 backlink for the key phrase with brand name included. Moreover, you can optimize the alt attribute of the images on the page with the key phrase or parts of it included.

Do you see any difference in visitors behaviour? Like lower avg time on page, higher bounce rate, ...

If for some reason large number of visitors bounce (pogo sticking in this case), it's good enough reason for Google to re-evaluate your page and move it (down).

To rank in the top 1 again you can do some things. Start to keep an eye on your competitors and how they make a difference and what methods they follow. Create as many high-quality backlinks as you can. And keep following the strategy you made to rank on SERPs.

You have to effectively improve all aspects of the website. After all, you will have to wait for the effects.

Are you internally linking correctly? no1 competitor probably has hidden back links.

You can try to make more backlinks.I think.

You should examine the pages' loading times because they may have an impact on their ranking and bounce rate.

I think you need to get more backlinks on targeted keywords and Optimize Image alt tags with descriptive text.

Getting to number one on Google can be an elusive feat. The best way to do it is to optimize your site for the search engine. A good sitemap can help push your site into the top ten, but you can also try the skyscraper method. The best way to do this is to figure out which pages on your site use the keyword you want to rank for. For instance, if your keyword is "air fryer," you may be better off optimizing your site for "air frying recipes." This way you will rank for all variants of the keyword, and you'll be sure to get a fair share of traffic from the popular keywords you're targeting.

You can also look at Google's Search Console for some clues. The company has tens of thousands of manual reviewers, and they will take a close look at the sites on top of competitive results. If your site is on the receiving end of these manual reviews, it's likely your rankings will drop off.

You could also try out Serptoday, a free plan that provides detailed information on which keywords your competitors rank for. It's also the easiest way to measure the effectiveness of your SEO efforts, and it's ideal for those without a big budget.

While you're at it, do a thorough audit of your site's performance. You'll be able to spot the top performers, and you'll know which pages aren't performing as well as they could be.