Is it shyness or social anxiety? How can I tell?

This is an interesting question. For me I feel shyness is more of this kind of statement “I haven’t warmed up to you yet” or “I’m very slow at trusting people” or “I need people to be vulnerable with me or feel safe around them first before I give off my vulnerability to them. Shyness is more of an awkward charm of a person or they can be described as someone who is innocent , awkward around discussions on topics that are taboo (e.g. sexual expression, dating). Shyness unlike social anxiety I would say is not consistent across all or specific situations (crowds, groups). A person who has social anxiety may have selective mutism (where they cannot talk in certain situations not out of choice but because their body faces a shutdown as they are reminded of a traumatic situation in the past). An example where someone can develop selective mutism, a component of social anxiety could be hearing/seeing a group of people laugh at someone. It can be so crippling for them that they lose the ability to talk for that moment.