Even when just copying what the professor what writing on the blackboard I could barely keep up.
It’s hard to summarize those lectures on the fly, and it might be a mistake as you’ll miss some important steps.
I found the exact opposite. My math and physics lecturers were expecting us to write what they wrote on the blackboards or overhead projectors down. So they had prepared the lectures this way, they wrote at a decent speed so you had time, and you could think about the steps as you transposed it to the notebook.
I found many small mistakes the lecturer had made this way, forgotten a sign or forgotten a factor, as I would follow along the whole time and go "wait, how did he get this from that".
I wrote it all down, but I seldom had to study them afterwards. I would often just gloss over and I would recall it all.
This was in stark contrast to other and later classes where the university administration had pushed hard for slideshow-based lectures. There the slides moved so fast I didn't have time to take proper notes, or I had to sacrifice listening to the lecturer. I ended up stop taking notes and just listen, but the memory of that wasn't as good as the handwritten notes, not by a long shot.