Realization: Transcribing jazz is transcribing on hard mode.
One of the things I've learned since I started my jazz piano journey as an adult learner several years ago is that it's far better to be able to learn something simple fluently and then add layers of complexity to it, than to learn something complex and find out afterwards that it didn't improve my fluency at all. This mostly only occurred to me in the context of learning standards and techniques ("Why would I think I can play Misty with rootless voicings when I can't even play it with shell voicings?").
But after reading many comments about how transcription is essential to developing my jazz skills, and subsequently beating my head against the desk attempting to transcribe relatively easy solos (with the playback speed set to 0.75x and painstakingly rewinding small sections over and over again), I took a step back and realized the same thing applies here. Why would I think I can transcribe a Wynton Kelly or Hank Jones solo when I haven't proven I can transcribe anything far simpler?
Since then I started with some extremely easy sounding pop songs, xmas tunes, and even nursery rhymes, and set out to figuring out how to play them by ear. I found that I can actually do this, and what's more it is even rather enjoyable when I've dumbed down my target sufficiently. I did that for several months and then came back to a jazz solo I was failing to transcribe and suddenly it was much easier.
This probably seems obvious to many but I am putting it out there in case someone is stuck like I was. Transcription is its own separate skill and it's not necessary to transcribe jazz as a starting point. It might even be a waste of time, relatively speaking. You might find, like I did, that it is far easier to transcribe jazz once you have transcribed easier non-jazz tunes. In the thousands of comments I've seen telling beginners that transcription is essential, I don't know that I ever saw anyone suggest that they start with non-jazz tunes if transcribing jazz is proving too difficult. So I am here to offer that as a possible option to my fellow beginners who may read this.