My son is 4.5 years old and can be a very cautious, timid child. He can also be a boisterous participator and initiator. Dynamic social settings challenge him. He requires a lot of time to settle in…sometimes longer than the activity itself!
My sense is that this is who he is and continuing to work on coping skills, including helping him name his feelings and choose how he wants to proceed sometimes from a couple of options I might suggest, is the best support I can give.

I’m seeing a couple of measures of success. First, he is very comfortable with daycare and gaining comfort with going to social events at our church. Second, he sees me express reluctance sometimes and he makes suggestions to me about how I might handle it based on what works for him.

All of that to say, I found your post comforting!