MacBook Pro OS Updates ?
Why will my MacBook Pro only update my to Catalina 10.15.7 and states no updates available?
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Probably because your MacBook Pro is too old for Big Sur.
From: https://support.apple.com/kb/sp833?locale=en_US
Mac Hardware Requirements
For details about your Mac model, click the Apple icon at the top
left of your screen and choose About This Mac. These Mac models are
compatible with macOS Big Sur:
- MacBook (2015 or later)
- MacBook Air (2013 or later)
- MacBook Pro (Late 2013 or later)
- Mac mini (2014 or later)
- iMac (2014 or later)
- iMac Pro (2017 or later)
- Mac Pro (2013 or later)