Most people live outside the US. So maybe change "World" and "Nation". Unless you are focusing on US only.

How can I filter out (block) subjects/words?

Yeah, the category names don't convey the meaning behind them very well. There's no intentional focus on US.

"World" includes everything that talks about two or more countries.

"Nation" is a category with news that touch only a single country, not necessarily US. The current feed is very US-heavy because practically everyone (even non-US sources) is talking about Trump.

Keyword blocking is available on premium: https://www.newsminimalist.com/premium#block-topics