I think episode length often depends on two factors: how frequently do you want to update vs how are your storybeats structured.
Using my own comic as an example: I post on a page-by-page(6-10 panels) basis to tapas, because I decided that I wanted to shoot for weekly updates, and on average I am able to produce pages at a rate slightly higher than my update schedule.
On Webtoon, however I post less frequently, an average of four pages per post(after they have been uploaded to tapas) that would be something around 30-40 panels per update depending. I break pages into contained story beats and try to keep relevant actions together. I could have posted on a chapterly basis since I had decided to shoot for bigger chunks for webtoon, but again, i decided to factor update frequency into my decision.
If breaking updates via storybeats is your jam though,(and you'll excuse the tangent) you might consider drawing updates with that first in mind(i chose to structure my story as though for traditional print comics). Creators well practiced in digital webtoon style comics will often take advantage of the episode format in the same way a novelist might treat chapters. There is room between episodes to allow for time between scenes(change in location, day/night changes, time skip), and provides a fluid way to move between scenes that may not mesh organically otherwise.
Of course there is no requirement to think about these things, its not even something I get the opportunity to think about when writing often because I have chosen to format my story in a way that does not rely on this easily. Its mostly something interesting to think about playing with.
