I only took a quick glimpse at a few comments here, so there's a chance I missed someone else say this already, but I'll post my two cents (sorry for the possible duplication): when I go to an interview, I'm not putting up a facade, I'm there to show 100% of me because if I pass, I'll probably stay there for the next year or so, meaning that being genuinely honest without thinking too much about putting up a fake persona is the best way to go for me. It's better to know incompatibilities right from the start than realise that you don't like the company 6 months in. So generally I don't get really nervous because I'm just showing who I really am, and if they don't like it, good, at least I know right from the get go.
Another thing I like to think about is that I'm interviewing them more than they are interviewing me. With every question they make, I think to myself "oh so that's what your company values as a good interview question" and I slowly start building a company profile in my head while answering honestly and to the best of my abilities.
I used to get a little nervous when I did exams at university, but I've come to realise that that nervousness came from me fitting a bunch of knowledge in my head a few days prior and fearing that some info would slip out of my neural pathways to make space for the color of the pen I was using that day, as brains do. I don't have this fear in interviews because, as I said, I'm not vomiting a bunch of knowledge I've forced accumulated over the past few days; in an interview, I'm just being myself and showing what I've naturally learned the past few years.
For those of you thinking that this is gonna decrease the amount of companies that I can apply for because of this "company profile" I build, yes that's true. Out of 10 companies I generally turn down 3 or 4 right from the first interview because I don't like them, not because they didn't offer enough money or because I don't like their tech stack. I just don't like their culture, and I make sure to confirm my ideas during the interview with some questions of my own. That's why I don't apply for most MAANGs, most of those have terrible company culture. If I'm gonna stay "married" to a company from 9 to 6 for the next year or so, I better make sure I actually wanna "marry" them.