Forgetting buddhism for a second and the fact that the picture of me right there is very skewed, your question is a good one: How would I know if I were wrong (about my problem not originating from within me)?
You're convolving what you've learned in psychology, which is that our view of ourselves is biased, with a lack of objective epistemological standard. This now becomes a bit meta, but I know I'm not imagining things because there's a prevalent lack of novelty in all my discussions and I have explored the alternative explanations the better part of a decade. When I host discussions among people of similar level, people tend to learn new things and exchange ideas that they've never thought of.
The obvious linear alternatives include that I cannot host meaningful discussions, I haven't made enough effort to look for engaging people, that I am too aggressive in conversation, that I am not aggressive enough, that I'm too rigid in my thinking, that I'm not rigid enough, that people aren't engaged, that I'm impatient, that I don't listen, that I take myself too seriously, that I haven't tried using tools that allow for more low-level discussions, that I shoot down ideas prematurely, that I suffer from duning kruger/hindsight bias/curse of knowledge/shared information bias, that I am too antagonistic, that I don't give people time to think, that my language is prohibiting me from accurately expressing my thoughts, that I don't convey my ideas properly, that I don't contribute enough to the conversation to set up a common domain knowledge upon which to build information, that I'm not entertaining or fluid enough, that I don't conform to other people's way of working, that I'm not connecting with concepts that I am unfamiliar with and thus consider them unimportant, and so on and so forth. Each of these presuppose that I couldn't figure it out over years of trying, and each one of your suggestions fall into this category, which is why indeed there is a prevalent lack of novelty also in this discussion, because you go for the straightforward linear explanations that everyone who would be in my position would've already explored, and then bootstrap every nuance that you pick up on and propose it as an alternative explanation; for example here you could pick up on the fact that I'm shooting down your ideas and offer as an alternative explanation to my decades-old problem that perhaps I have never tried not shooting down everyone's ideas, as though I was not self aware.
I'm not ungrateful. However, I try to first and foremost be clear. If we really wanted to get into it, there are also other standards that at least suggest that I'm intelligent, but I, like you, do not appreciate anyone gloating over their academic and intellectual achievements so let's just leave it at us both knowing what I'm talking about
So yes, like I said before, I am a part of other internet communities which are for "intellectuals" like for example slatestarcodex and I've taken the last 10 years to seek intellectual company IRL. The same problem applies also to your suggestion to consider the nuance of what a sportstar vs a nutritional expert might have to say about fasting and to consider the fact that perhaps other intellectuals aren't having the same problem (there are some examples); you're missing the point.
The whole sportstar vs nutritional expert thing you mentioned is of course true and interesting in its own right. My personal philosophy on all of this is something akin to connectivism (and part mysticism), but the point is that 95% of everything exists in our shared reality and only a small percentage of people can go beyond the immediate horizon to explore any question, and even smaller percentage exists in a reality that is less shared, because only few people truly introspect.
So while I appreciate that a sportstar have different nutritional advice from a nutritional expert, the personal nuances at best color the topic, but truly novel ideas require deep thought and introspection, and a sportstar jacked up into the wide web for the most part will not have gone significantly further beyond the horizon of the collective knowledge.
I already know the left-wing and right-wing talking points, I know what the apologists say about God, I know what the atheists have to say in return, and so on and so forth, and while I appreciate hearing the same things over and over again (with slightly different "colors" painted over a global adiabatic evolution of knowledge), I appreciate even more when I hear something fundamentally new. Yesterday, I was chatting with one of my students over lunch, and he told me something very interesting. He said that people in the past used to have more imagination, and he recommended I read the Time Machine by H. G. Wells. What I think is possible is that the collective knowledge around 100 years ago was so fundamentally different that reading some of the old sicifi book exposes us to a shared reality of knowledge that no longer exists within our society, so it "feels" novel. At least that'd be the connectivist view. But maybe we've since then also become too attuned to having all the information accessible to us, and we've put all our efforts into keeping up with the constant stream of information, being spoon-fed all sorts of garbage about how to live instead of sitting down and thinking about life ourselves, in the process forgetting the prime directive. Who knows.
To answer your question about me being unable to point towards anyone else having this problem, I believe it was J. Peterson who said something similar about leftist talking points. I don't particularly like J. Peterson or appreciate him as a person, but he did give at least some originatlity to the age-old political debate. I couldn't find the youtube video anymore; I think it was that channel 4 interview or the CG shitshow where he said it.