Upgrade from High Sierra to Big Sur fails to install

I have a 2017 Mac Book Pro running High Sierra with over 100GB of storage space available. I'm trying to upgrade to Big Sur.

1. I go into the App Store and select "macOS Big Sur" (12GB) and click on download.
2. It says downloading and then calculating and appears to finish after about 30 seconds and then presents an open button.
3. I click on the "open" button and the window just flashes but does not do anything.
4. I've done several reboots but nothing seems to change the behavior. There are not errors or warnings anywhere that I can see.

What am I doing wrong? Thanks in advance.