On retention, the honest answer is that it is real and it is mostly not about the format.
The variable that matters most is what else you are doing. Listening while driving in traffic, or working, or doing anything that takes real attention, means you are genuinely absorbing less, and the book keeps playing regardless. A page waits for you; audio does not. That is the mechanism, and it has nothing to do with hearing versus seeing.
What helps, in order:
Match the book to the activity. Demanding books for walking or washing up. Familiar or light ones for anything that takes concentration.
Slow down. People push the speed up and count more books. Comprehension falls off well before it becomes uncomfortable, so you feel fine while retaining less.
Say something about it out loud at the end of a session, or write two sentences. This is the same principle as writing after reading a paper, and it does most of the work.
Rewind without guilt. The main advantage of the page is going back. You can go back too; you just have to decide to.
And the honest trade: a book heard while commuting is competing with nothing, not with the same book read attentively. Twice as many books at lower retention is a clear gain over the hours you actually had.