Currently, Australia holds the record on having the highest duty free threshold: A$1000 ($703 / £525 / 626€) since both US & EU rescinded theirs recently (the UK is planning on removing de minimis, at the moment it stands at £135 or below duty free). I mean, do travelers (bringing in stuff they purchased elsewhere) and importers (who bought stuff online from overseas retailers) now have to pay extra taxes in the US & EU?

Has it actually been enforced already? You only notice it when you either travel and bought stuff (unopened and brand new) whilst on vacation upon returning back to US & EU they hit you with those charges or buying stuff across borders as the package is being held at customs waiting for tariffs to be paid. Is this just an excuse for their governments wanting to extort money from citizens trying to deter them from buying stuff abroad?