James Harden doesn’t travel, he simply knows the rule book better than non-experts. Specifically, he knows the gather step better than most anyone: https://www.sbnation.com/nba/2020/2/23/21149538/james-harden...
What you don’t notice is that the gather step is used for many more movements other than a euro step, but the euro step also has a change of direction and change of acceleration that combine to make the movement look illegal to someone who doesn’t understand the rules.