Conclusion

Udemy alone is not enough — you absolutely must also do the Killer.sh practice exams!

My Journey

December 2021: First touched Kubernetes at work. Had zero knowledge and had no idea what was going on.
January 2022: Bought the "Kubernetes Complete Guide." Read it bit by bit while looking things up online. Gained a rough understanding of Pods and Services.
February 2022: Bought a Udemy course in early February and started studying for the CKA. This course is excellent — highly recommended! Watched all the lectures, then went through the Practice Tests twice. Also did the Lightning Tests and Mock Tests twice each.
March 2022: Took the CKA for the first time at the end of the month. Had trouble getting the exam started and panicked. Wasn't used to the multi-cluster format and ended up working without SSH-ing into nodes, which meant I couldn't solve problems properly. Panicked even more. Failed with a score of 58 (66 required to pass).
April 2022: Couldn't find time due to work and job hunting. Didn't feel like studying either. Somehow carved out time to study. Looked up how to pass and discovered that Killer.sh practice exams come bundled with the exam for free. Did the free Killer.sh questions and practice exams twice each. Also did the Udemy Lightning Tests and Mock Tests twice in parallel. Retook the exam in mid-April and passed with a score of 92.

The CKA exam is worthwhile
You learn the fundamentals of Kubernetes
Come to think of it, the CKA isn't that difficult
Actually typing commands during the exam is fun and helps retention — love it! Wish there were more exams like this
Mumshad's Udemy course is excellent!
Killer.sh is excellent! — The CKA exam has aliases set by default. k run test-pod --image=nginx works fine
If you just want to pass, you don't need to buy a book. Udemy alone is enough
Just in case, bookmark kubernetes.io