I have installed Big Sur on my Macbook Pro's internal drive (personal use) and I use an external USB3 SSD drive with High Sierra on it for work.
When I still had Catalina on my internal drive (and below), and when booted into my High Sierra session, I could go into System Preferences, and select my internal drive as startup disk.
Now, however, with Big Sur, I get the message that the internal drive is no longer recognised by High Sierra, and so I cannot select it as a boot drive anymore.
On my MB Pro, this is easily overcome by pressing the Option key at startup, but on my iMac, where I use Apple's Bluetooth keyboard, I can't use that option.
I haven't installed Big Sur on my iMac yet because if I cannot boot into High Sierra and then back to Big Sur anymore on that machine, I'm well and truly buggered.
Any suggestions ?
When I still had Catalina on my internal drive (and below), and when booted into my High Sierra session, I could go into System Preferences, and select my internal drive as startup disk.
Now, however, with Big Sur, I get the message that the internal drive is no longer recognised by High Sierra, and so I cannot select it as a boot drive anymore.
On my MB Pro, this is easily overcome by pressing the Option key at startup, but on my iMac, where I use Apple's Bluetooth keyboard, I can't use that option.
I haven't installed Big Sur on my iMac yet because if I cannot boot into High Sierra and then back to Big Sur anymore on that machine, I'm well and truly buggered.
Any suggestions ?
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