I have seen RemNote… but I think it needs a bit more polish before I can really want to use it. The way they handle flashcards is interesting, but I didn’t enjoy using it as much as I wished I did!
As for making flashcards… it can be time consuming. What I plan to do is create the cards as I make notes. I’ll be creating the cards in Excel and then importing them into Anki.
There are apps that can make integrate flashcards into your workflow easier. Polar Bookshelf can make an Anki flashcard directly from a highlight within the reader. That can easily save you a lot of time.