The correct stance is the distance (wherein one is considered a traveller) returns to ones Urf (what’s customary or commonly known with his people)
Imam Albani said, “and the truth is (that) there is no specified limit for the travel in the arabic language nor in the legislation”
Then he mentioned it goes to what is customary with the people
As for how many days (after which one is considered a traveller), then if you are not in a state of doubt regarding your travel and you are certain you are going to stay a certain amount of time, then four days.
If you go somewhere not really knowing when you will return, whenever Allah makes easy your return, you will leave whether it is today or tomorrow while you are not certain about (how long you are) staying, then this case is what is narrated from ibn Abbas which mentions 19 days.
And some Sahaabahs even reported being considered travellers for 6 months in a place where they were stuck and didn’t know when Allah would make it easy for them to leave.
Also here a benefit I translated on the length of when a traveller can shorten his prayer. In it is the mention of many of the opinions regarding that and its proofs taken from the works of Shaykh Muhammad Ibn Hizaam
Allah knows best
Majid Jawed Al-Afghanee