I would think that 2-3 projects is somewhat excessive; I think doing just one project in a large amount of depth is better than multiple in less depth. I only did one project myself (it wasn't exactly the best in the sense that I achieved literally 0 useful results, but I sure as hell didn't say that on my personal statement. Also doing multiple would have killed me in terms of time commitments). Unfortunately I cannot recommend anything to do with cyber security, as that is something I don't really know much about. However, if that is something you are passionate about then it should be easy enough to learn about it and find something that is interesting enough to warrant doing a project on. If for example you are more math oriented, perhaps learning about cryptography is useful or zero knowledge proofs, but again do something that is worth it for you, not because some random stranger told you to do it.
Also, don't worry about being worse than other applicants. There's nothing you can do to make the other applicants worse (unless you were to do some slightly illegal activities), only to make yourself better. I can guarantee that there are people who are very mediocre in terms of achievements (potentially myself included : p ) who got in despite not having created the matrix at age 4 or whatever else you think the average Cambridge student has done. In fact you would be slightly more decorated than I would be as I only got a silver in the SMC in year 12.
Finally, nowhere in the application process does it state you need to have certain projects under your belt, or know any programming languages. Whilst they certainly do help, they are only a part of your application, not the whole picture.
Also, I should hope this goes without saying: this is all my opinion, I make no guarantee this will help you get in, bla bla bla.