This is a difficult thing for sure because we all know most people mean well. It's also difficult when someone has specific experience in that condition and they're just trying to help. I have a friend who has a condition that I also have (not MG) and I'm also a specialist HCP in that condition, my job is literally giving advice half the time, I'm also astutely aware of how annoying unsolicited advice can be. We have a system where if she or I are having a difficult time we basically say whether we want the advice or not. Or if it's unclear I will say 'do you want my sympathy or my advice ' (obviously less abruptly than that).
Try and remember that they all mean well and most of the time comes from a place of love but starting a conversation about giving advice and how that's communicated between you might be helpful. An example being just saying somethibg like ' sometimes I just want some sympathy, because sometimes that is all we need, we don't need 'fixing' we just was some TLC, sometimes we want advice ....' and go from there . To be fair to the other person we can't expect them to be psychic and know that, so communicating that to them is only going to be helpful.
Strangers is a whole different ball game , I have no idea how to deal with strangers unsolicited advice. I tend to just be polite and think I'm never going to see this person again.