The upgrade MacOS Big Sur will not download.

Because it's too old to support Big Sur.

Tinnyvb wrote:

why can I not download macOS Big Sur to my MacBook Pro (Retina, Mid 2012)?

It doesn't download because it's not supposed to download.

Maximum OS for your computer is 10.15.7.

mmariee wrote:

I have the same problem! Do you get any message saying the update failed, or does nothing just happen? (as it does for me) (I have a 2017 MacBook Air though)

See: How to upgrade to macOS Big Sur - Apple Support

I have the same problem! Do you get any message saying the update failed, or does nothing just happen? (as it does for me) (I have a 2017 MacBook Air though)