Welcome to planDisney, Jan!
Thanks for choosing to be our Guest. You've asked some great questions here.
Typically, if you travel to Walt Disney World between the end of November (right after Thanksgiving) and mid-December you should be able to experience the Christmas festivities without the largest crowds. To be honest, there aren't any non-busy days at Walt Disney World. However, in my experience, I've found this to be the best time to go. I see that you're arriving on November 21. The week of Thanksgiving is usually very busy (Thanksgiving Day is especially busy). I'm sure you'll still have a fantastic time. Just make sure you utilize
Disney Genie+ and arrive at the parks nice and early. If you're staying at a
Disney Collections Resort hotel, take advantage of the
Early Theme Park Entry (and
Extended Evening Hours, if you're staying at a Disney Deluxe Resort Hotel or a Disney Deluxe Villa).
Figuring out the best day to visit
Disney's Hollywood Studios is tricky. Due to the extremely popular
Star Wars: Galaxy's Edge, this park usually reaches capacity well in advance. However, Wednesday seems to be a good day to visit if you're looking for lower crowd levels. Still, I don't think there's a ton of difference either way. In fact, Tuesday, Wednesday, and Thursday are probably the best days to visit the Disney parks if you're trying to experience lower crowds.
Tickets are also sometimes cheaper mid-week too.
I hope that's helpful, Jan! I hope you have the most wonderful time of the year at The Most Magical Place on Earth.
Mike