I implemented a tx_news filter to filter multiple categories with this code: https://docs.typo3.org/p/georgringer/news/main/en-us/Tutorials/Templates/MultiCategorySelection/Index.html
This is working fine with some little customization here: https://2022.asienhaus.de/themen/
The filter is using OR to filter categories: Filter news with CategoryA OR CategoryB Is it possible to filter with AND: Filter news with CategoryA AND CategoryB?
Thank you for your help. Jürgen