Why did I get a sudden drop of impressions and clicks?

I have been working on a new website. For Context I added this site to the search console and gained visibility already within a couple of days, this visibility completely dropped and I don't even appear on the first page anymore for my own "brand name". The domain existed before which I didn't know about. (Was a spanish site, mine is not but same niche) Most traffic I got was initially for a tool I developed basically a calculator. There is no sitemap, I wanted google to crawl and index pages on its own. Currently google indexed 900 pages on its own (single pages for listings from 20k, with appropriate schema https://developers.google.com/search/docs/appearance/structured-data/job-posting) [https://imgur.com/z1rM6Db](https://imgur.com/z1rM6Db) Should I manually remove these pages again and block them via robots.txt?