This sounds like a common autistic experience. I brought similar concerns to my therapist because I was terrified that I had been harming people without knowing it. Her response sounds super trite and I didn't believe it but she said that the fact that you are concerned about this is an indication that you are not a narcissist (both in terms of clinical and popular definitions).

suspect I might be correct on a narcissism related self-diagnosis too, I have heard from someone close I overestimate myself,

Ooooof, that just sounds like they are being mean or judgey.

also, I obsess with "self-mastery" "transcendence" "enlightenment" etc.

That sounds pretty normal. I've been introduced to the poorly named concept of optimization OCD which might fit what you are describing.

which might also just be coping for the autism experience of being misunderstood and wanting to transcend that.

This is what I think it is in me. Before I knew I was autistic and before I knew what masking was I was sure I could fix whatever was wrong with me by just trying harder and mastering all the self help, pop psychology, etc. I never apply the idea of "bootstraps" to anyone else, but I'm a different story!

I do think one of the main reasons allistic people may see autistic people as sometimes displaying narcissistic traits is that they are speaking a whole different unspoken language than us. There are signals of safety and belonging people give each other and those are very hard to crack and adopt if you are autistic, almost by definition! I think it's kind of like saying someone who can't read english is illiterate even though they can read in the language(s) they are fluent in.