As I just noted, and it's important to hear this: Narcissists can and will seek out the strong.

It isn't enough to be strong. As you noted, and I will note more specifically, there are some very particular red flags that go along with narcissistic abuse that must be learned in order to spot it in a timely fashion, i.e. before it becomes brain worms and your own psychological well-being starts to deteriorate. It isn't a generic thing about knowing how to say no, though obviously that is part of it.

It's about informing your threat detection systems and trusting them. This is not easy to learn.

Nor can one or two articles like this cover it, but it's way better than nothing for anyone new to these behavior patterns:

https://www.psychologytoday.com/us/blog/toxic-relationships/201709/how-spot-narcissistic-abuse

https://www.insider.com/strengths-narcissists-target-in-their-victims-2018-6

It takes practice. Unfortunately the opportunities will be there, because evidently these people are everywhere now.