After updating to MacOS 11.1 - Unable to check for updates

Thank you! Turned off Clean My Mac and voila! Everything worked.

Try testing from a new user account.

Also, rather than using a USB Bootable installer in case it's corrupt, try downloading and running a new copy of Big Sur.

Or reinstall from Recovery Mode.

Enabling "Automatically keep…" might help.

Just to add, are you running any antivirus, security or other junkware on your Mac such as CleanMyMac?

You're welcome. You should uninstall CleanMyMac.

I've never had it installed but try this…

https://cleanmymac.com/how-to-uninstall-cleanmymac

It would seem there is not acknowledged Internet Connection or it is too slow to connect to Apple Servers as outlined in Original posting " Unable to check for updates Make sure you are connected to the Internet."

As @dialabrain suggested plus notice Advance icon in screen shot >> open it and check / enable all options if desired .

Gabi__S wrote:

[I've ruled out #2 corrupt USB installer or corrupt Big Sur download]

How did you do that exactly?

FWIW, I installed Big Sur onto an external SSD from an iMac. It boots the iMac without a problem. Plugging the same SSD into a new MacBook Air refuses to boot. Just food for thought.