Can't update to Big Sur

Hi, Dadjustice.. I think you have to go look for it in the App Store… are you referring to Big Sur or an update to Big Sur, eg, it’s already installed on your iMac ? … before you do that, make sure your iMac meets Big Sur’s requirements, and you should be good to go:

macOS Big Sur - Technical Specifications (CA)

john B

It can be that your Mac ,model is too old to run Big Sur. Go to apple logo in menu bar>about this Mac to check your Mac model, after that compare it to this list

macOS Big Sur is compatible with these computers – Apple Support (UK)

What year model is your iMac?

see > Identify your iMac model - Apple Support

Have you tried getting Big Sur,

from > How to download macOS - Apple Support