Clickbait remover uses YouTube’s auto generated ones, which while are seemingly random, are not. They use some algorithm to target faces in exaggerated expressions.

DeArrwow uses actually random ones (and then a user can submit specific timestamps if there is a better one). It’s noticeable better on many channels imo. It also let’s us do things like make sure the random thumbnail is not in a sponsor using SponsorBlock data

(I made DeArrow)