for proofs i really liked two sources: susanna epps’s discrete math book and also rosen’s discrete math text (though epp’s is friendlier for the beginner)
supplement those books with these lecture videos:
https://youtube.com/playlist?list=PLl-gb0E4MII28GykmtuBXNUNo...
they appear to follow rosen but they’re the same topics you’d see in epp
if you’re the complete beginner go with epp and then use rosen as a supplement.
if you are an advanced undergraduate in math but don’t know category theory then:
https://math.jhu.edu/~eriehl/context.pdf
or
Basic Category Theory by Tom Leinster
(even though i’ll list a bunch more resources below i’d probably start with leinster and work up enough math maturity to push through it.)
i also liked this: https://arxiv.org/pdf/1912.10642.pdf
if you don’t know advanced math then there is an upcoming (not yet released book) called “the joy of abstraction”
i cannot attest for the book as i haven’t read it but may be good for true beginners:
https://www.cambridge.org/us/academic/subjects/mathematics/l...
(click “look inside”)
they say “no formal mathematical background needed”
you can read the description and see if that is something that would be of interest to you.
this guy has videos + a book
https://youtu.be/fY02LIW8fvk
there are a lot of books like “category theory for programmers”, “programming in categories” and the “seven sketches” books along with lecture recordings and videos that you may find helpful.
category theory for programmers might be the easiest of those three books. i worked a bit out of the programming with categories (http://brendanfong.com/programmingcats_files/cats4progs-DRAF...) book and ignored all the haskell sections and just focused on the math parts (this is a distinct book from “category theory for programmers”. people confuse the two due to the names and the fact they both use haskell).
if you know category theory and want to learn topology then there is “ Topology A Categorical Approach” by bradley et al.