I have a couple of methods. One is Goodreads, which you can access either through their website or their phone app. I also have a “books” folder in my phone photo library, where I take pics of physical books that I find interesting and want to remember later. I go through that folder on occasion and tag the ones I’ve read so I can separate them out. I’ve also used the website fantastic fiction, but it’s not as great for the “to read” pile as Goodreads.