Tale of two computers...
My work MacBook Pro, hardwired directly into my home router, is doing what everyone else is reporting - seemingly stalled and updating in small increments every now and then. I am upgrading from the latest version of Catalina to Big Sur on my MacBook Pro.
My personal iMac, which is connected to my home network wirelessly AND was running the public beta of Big Sir, is merrily downloading normally it appears. I started the download for it 10 minutes before the one on my MacBook Pro and it is already ahead of it 5.81GBs to 346MBs.
Sure hope I can copy the downloaded installer from my iMac to my MacBook Pro (and other computers that need to be upgraded in my house.)