My own personal anecdata on this comes from being able to find a passage I read in a 500-page book in 1992 for a class I was taking in 1998. I could probably even find that same passage now if I were to walk across the room to the bookcase where I have that book.

Although on the other hand, I was also able to turn up an article I’d read online a couple years later when it was relevant to a friend’s relationship with her newly out trans kid, but it was definitely a different sort of recall and lookup happening in the latter case.

While physical "progress bar" is much easier to remeber than digital one (on the side of the screen for pdfs), because you actually interact with it the whole time, i don't find (ha) finding a particular passage hard without it. I personally usually can remeber a phrase or just a word and search for them in a PDF to find the needed passage.

It's pretty easy to highlight passages with most e-reader software. Some even let you write a note that goes with the highlight. You can then look through a list of all highlighted passages.

It's when something comes up and you remember that you read something relevant in the past. In most of those cases it's not about "Ah, this is something I may want to check again at a later time, so let's highlight it". So, there's no list of highlighted passages to search through.

Indeed this is one of those things I miss about paper books. When the above happens I have a terrible time finding that on my Kindle. Most of the time I'm not able to, while with a paper book I didn't have that problem, mostly.