How to deal with the (hidden) feedback from research supervisor? I am a PhD student who works in a theoretical field. Often times, I have discussions with my research supervisor, and I try to do as much work as possible.

It seems that many times these days my research supervisor does not seem happy with my performance. He often doesn't seem satisfied, judging from his facial expression and body language, but when I ask him, he just says ok. Most times, I leave the meetings in illusion (meeting was good or bad). I feel pressure due to these things. I don't know if it is a common thing in academia or not.

Question:    How to deal with the (hidden) feedback from a research supervisor? This is constantly creating pressure on me.

There is a difference between feedback and hidden feedback. For explicit feedback, we can ask the supervisor once in a month or something like this.
Actively ask for actual feedback.
Of course, you need to be prepared for any feedback that is to come.

I am reading things into this... but I suspect you are reading feedback into their facial expressions and body language because you in fact need more feedback.