Most likely, you sent us the URL after pressing the search button. If you visit the category page, you should see the correct URL (e.g., site-sample/listing-category).
Also, you can change the permalinks in WordPress Dashboard > Settings > Permalinks.
https://findyourretreat.de/?post_type=hp_listing&latitude=&longitude=&_region=&s=&location=&_category=79 - This is a search link, it cannot be changed through Settings > Permalinks (it contains various parameters such as location, region, category, etc.)
Permalinks change the URL of specific pages, such as Listings, Hosts, etc.