example (but need to find binaries, I bet there are archives for crackmes.de)
https://www.aldeid.com/wiki/Solution-LuCiFeR-First-CPP-Crackme
more complex: https://bin.re/blog/crackmes-de-lescos-keygenme-2/
one more

input: https://raw.githubusercontent.com/apachecn/crackme160/master/AfKayAs.2.zip
solution: https://blog.csdn.net/csg999/article/details/104050697