Biden supporters with the American flag? No, many of them shun it. That's a Trump supporter thing. (Yes, there certainly are some, but a great many of them don't.)
Note that Bernie dropped out of the primary and endorsed old Joe. So most of his supporters are now Biden voters.
And you made this assumption based on...?
Well well well... hypocrisy much?
Oh, and there it is! The appeal to emotion! The Nazi flag has a very lear cut connotation. National Socialism. Period. But the Confederate flag means different things to different people. Sure, some may take it to mean white supremacy, and some even use it that way, but some people fly it to honor ancestors, some for historical reasons (I own all the National flags, as I collect old flags), and, again, some people just fly it specifically because liberals don't like it. Again, I'm not defending either flag, but there is a distinction to be made here.