Big Sur - Can't get on MacBook Pro 13" (Early 2015)

Big Sur is out there on the App Store.

How to upgrade to macOS Big Sur - Apple Support

Make sure your mac has at least 35.5GBs of free space.

Have your mac connected to your router via cable.

Go to Section 2 and click on Get macOS Big Sur

this will redirect you to the App Store, give it a minute or two

and open the Big Sur download page it should say Get.

Pressing Get will probably open the System Preferences> Software Update

panel and start the download.

Do not use the mac while it is downloading or any other devices that share the same

internet connection.

Have you checked that any third party apps you use in Catalina will still work in Big Sur.

Also check that any third party hardware, printers/ scanners etc have drivers available

so they will continue to function in Big Sur.

Would suggest re-verifing the age of this computer and make sure it is MBP 2015 - About this Mac from Desktop. If indeed 2015 and have the 36 GB of Empty Space Requirements ( suggest 50 - 55 GB ) and the Apple Apps. Store is not being friendly >>

In Terminal " softwareupdate -l  " without quotation marks and will search for updates and list available for this computer.

If the output is showing Big Sur 11.5.2 ( latest version - good )

" softwareupdate --fetch-full-installer --full-installer-version 11.5.2 " again without quotation marks. This should bring down the Full Version of Big Sur and install a new Application in Applications folder called Install Big Sur.

Suggest stopping there and do a Time Machine Backup as a Safety Plan. Once done - disconnect all external devices and restart in Safe Mode which does a Repair Disk, clear cache files and only loads Apple Software - load slowly - Normal. Once logged back in - run the Big Sur Installer and follow all the prompts.