Traveler does have an official title in Fontaine, and Liyue.

I completely forgot about this. Like the "Honorary Knight of Favonius", they're the "Honorary Senior Research", or just for fun you can extend it to _"The Honorary Senior Researcher of the Fontaine Research Institute of Kinetic Energy Engineering."_ It's when you do the Research Institute world quest. Most youtube videos or shorts, when they compile all the titles the traveler gets in each region when they get to Fontaine, I usually use a non official title, like's "Ludex's Executioner" or "Fate's Executioner", it's probably because this is an unvoiced world quest, while Mondstadt and Sumeru's titles were given during the Archon Quest. Also, even in Liyue, we do get another title of "Sergeant" during the opening cutscene of the Stygent Onslaught when it was first introduced, also this might not be official title rather an appropriate title for emergencies, still something. Those compilation youtuber need to get on this.