An interesting question. I think that the bar is so low for feedback that any type of feedback is pretty welcome. For my most recent job search most of the time the company never bothered to tell me that I was declined, they just left it open. Something like: "Thanks for coming in today. The team had really positive feedback and we'd like to invite you back for another round. [so and so] will email you in the next couple days..." followed by weeks / months of radio silence despite followup.

The best feedback I got (through a side channel) was that the team was in a deadlock between me and another candidate, so it came down to a coin toss and I lost. I felt reassured, because at least the ordeal was over.

Another time I was declined because they only higher product managers with CS degrees and I do not have one. In that case I felt annoyed because this info was readily apparent on my resume, and I do have tech skills but they never brought up the issue in the interview.