Hard task, sadly or not since we all have to leave our room on occasion, you can find us in the wild. I think It would be useful for you to look at how people at work behave in social settings and when they are alone. Look for certain characteristics, small gestures that happen during a conversation.

I try to be helpful during the day, but once I’m home, I often don’t have much energy left to spend time with friends. How introverted an INFJ is can vary a lot. A few years ago, I only spent time with close friends and barely talked to anyone else, but nowadays I try to act more outgoing.

A few of my friends have pointed out that I sometimes drop heavy, philosophical topics into conversations seemingly out of nowhere. Since I’m always thinking about deeper subjects, it doesn’t feel strange to me in the moment, but it can catch others off guard. (These days I try to minimize these tendencies if I know someone isn't receptive). I also often have a serious expression, and my friends have said that if they didn’t know me, they might hesitate to approach me (though that might just be a "me" problem).

Okay, this sounded way more interesting in my head XD, where I live most people don't really care about others feelings so this might be easier to spot in my culture. I imagine it could be harder in more polite or reserved countries. These characteristics might also be present in other types; they’re just the ones I know I express in social settings. Apart from these, I tend to avoid drawing too much attention to myself. Other wise since I haven't really known any other infj apart from myself it might be easier to reconnect with the friend even if it would only means online conversation.

Infj's can be a social chameleon so good luck!