The definition listed online in dictionaries reads as though it was defined by someone who did not really know what “doom scrolling” was - they understood what “doom” and “scrolling” were independently, so they made the claim that the “doom” in doom scrolling had to do with the themes and tone of the content, where in my experience online the “doom” in doom scrolling actually represents then endless and mindless consumption of vapid content. Existing in a state of mindless repetitive dopamine scrolls equivalent with being “doomed”, the stagnation of other pursuits for the nothingness of scrolling, I could go on. This is all my opinion of course.

I think the proper definition for doom scrolling has been mentioned multiple times by others in this thread and it would be something like:

Rapid consumption of mobile short form content for extended periods of time, often with no end goal in mind.

Others have done better than me, but that’s my two cents.