My little one was quite picky about food items but with time I built curosity in them by trying that food first and acting surprised so that they can be curious to try it out instantly. This has been working for me as my little one loves to copy me in everything.
I get it, my kid is super shy too, and I worry about the same thing. We started with just one friend over at a time, not big groups. I also try to talk to them about how they feel, like if school or making friends feels hard. Little things like saying “hi” to someone, even though it’s small, helped a bit. It’s slow, but I think it gets better bit by bit.
