I installed Beta Big Sur yesterday (10 Aug.) over beta Catalina on an external SSD. A hefty 12gb download, I might add! All went well. I was able to boot Into Big Sur from the external drive. BUT, when i booted into Mojave on my 2014 iMac, a warning came up that the external drive partition was not fully compatible with Mojave. I clicked continue and Mojave mounted a partition that contained none of my data but had the same capacity of the Big Sur installation. I chalked it up to a new ‘flavor’ of APFS which is not visible to previous systems to Big Sur. Can someone clear this up for me?
geoMac
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I installed Beta Big Sur yesterday over beta Catalina. 12gb download! All went well. I was able to boot from external drive, but when i booted into Mojave on my 2014 iMac, a warning came up that the external drive partition was not compatible with Mojave. I clicked continue and Mojave mounted a partition that contained none of my data but had the same capacity of the Big Sur installation. I chalked it up to a new ‘flavor’ of APFS which is not visible to previous systems to Big Sur. Can someone clear this up for me?