I should preface this with, I'm not a Note user, however I will say that screen wise you probably wouldn't notice the difference unless they were side by side. It's obviously going to be a step up from where you are now but the difference between the two, screen wise, is something you would only really notice with both in front of you and it has the 120Hz that everyone seems to be going crazy for right now. The only thing that it won't have is 120Hz at the highest display rate.
As for the camera, it's my understanding that they fixed a lot of what wasn't right when they went from the S20, which was laden with issues, to the Note 20 and I've heard the Note takes decent pics and videos. The S21 has a higher actual zoom, 10x vs the 2x or 4x of the Note. Not talking the 100x which is digital on either. Plus it's a Note so you get all of the upgraded little goodies that go along with the new S-Pen and all of that. Where as the S21 is just S-Pen compatible. It isn't the full S-Pen experience, as of yet. It also requires a bulky case to carry the S-Pen and the phone as a package. I have heard that they are going to bump some of the S-Pen functions later but even then it won't be what you'd get with a Note.
If you want to see the two devices side by side there are actually several vids on YouTube comparing the two. Actually I can't think of many devices that haven't been compared to the S21. It's the hot new kid on the block right now. Several reviews have said that they got a lot right with S21. A few things to note about that however are the three things that everyone is talking about, no headphone jack, no SD and they've actually taken usability away from Samsung Pay on the S21. Where Samsung Pay used to work virtually everywhere it now only works with NFC reader enabled teller devices. I really think comparison vids are going to be better resources for you because everyone has their favorite and there are more than a few diehard Note fans and a lot of S users don't get what makes the S-Pen worth it. I have the S21 Ultra and don't have any intention of getting the S-Pen or even know what Note users see in it.