Updated Catalina to Big Sur but on reboot it reverted to Catalina

I have a 2019 16” MacBook Pro and tried to update Catalina OS to Big Sur using update from preferences. I was connected to WiFi and everything looked normal with no errors on install. I saw the Big Sur desktop graphic but when the computer rebooted it reverted back to Catalina, now the latest version. Has anyone else seen this?
Updated Catalina to Big Sur but on reboot it reverted to Catalina
 
 
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