Hello, guler98faruk
can't really help, but I've been observing a similar pattern for many years.
On some sites, after Google updates, traffic drops to zero, on others, it comes back.
I have no idea why this happens and have stopped trying to find patterns. I just wait about six months until a new update occurs and the site recovers. Some sites never recover.

I've noticed this happens with 'small' sites, where daily traffic is up to 10k.
The age of the domain doesn’t matter, this happens even with domains that are 10+ years old

Maybe someone can give advice regarding the links.
I don't have experience with this

It could be related to the recent change noted here: [webmasterworld.com...]

Now Google tools and other rank-check tools that rely on Google services were limited to 10 results rather than 100 as formerly used. So whatever method you use to track rank or keywords may not show more than 10 results.

I would not make sudden changes to try to get to the way it was before.

First, Don't Panic!

g's updates are for g ... not webmasters. Every once in a while the update goes too far and collateral damage occurs. This is usually corrected in the next update... weeks or months down the line. Do know that EVERY update by g is designed to narrow and nail down any income loss for g/advertisers so former traffic RARELY ever returns---better, but never as good.

Those of us around since the beginning have seen this cycle on a routine basis. Every year the keywords have been diminished (due to abuse among other things) and it looks like g is about to narrow it down even further. Keywords still work, but keywords that are NOT really consistent with CONTENT and INTENT are likely to be deprecated in the future.

Plan accordingly.

Meanwhile, just make sure your content is unique, fresh, ORIGINAL, and fills INTENT.

As of September 17, the number of ranking keywords dropped from 6,000 to 1,000. There are no manual actions in Google Search Console, and there doesn’t seem to be any indexing issues. However, for some pages, keywords have almost completely vanished and can’t even rank within the top 100. In this case, what steps should I take?

Work with the 1,000 left until the next update takes that number down to 60. Keywords ALONE are not the answer to web success. Work on content, community, and brand. Become UNIQUE. Be of VALUE.

Meanwhile, don't do something stupid chasing keywords. That might make the present situation even WORSE.*

^{*Old school advice, been there, done that, since 1996.}

Any idea what this "spam update" looks for?