Whatever fits. I personally prefer at least a number (partly because upload order is not always accurate).
Some stories lend themselves to detailed chapter titles, some to single-word ones or just numbers.
I had one story (sadly lost after multiple computer issues) where each chapter had the name of the narrator (as each was in first person, from a different character's view point) and a number.
Another, for a different site, only has text terms because they prefer their own auto-numbering system.
And one I have on Royal Road has chapters numbered as "Case File #-#: Descriptor" as each "story" in the book is a separate case file for the character, so the first # is the current case file (at the moment "stalled" at the second due to other stories taking over my time, so either 1 or 2) and the second the chapter within that story.
So - whatever feels right for the story.
Note that some sites (like HoneyFeed, the one that prefers to autonumber, or PocketFM, which does not like you to title chapters at all per their guidelines, just to make sure there are clear chapter breaks) have specific requirements in place as well.