108 MACWORLD JANUARY 2022
HELPDESK MAC 911Since then, many people have asked
about what seemed to them a bizarre,
unnecessary, and inaccurate
requirement—that is sadly absolutely true.
Does an iMac have to be running an old
version of macOS as well to support Target
Display Mode? Yes, it must. And so must
the Mac connecting to it!
Apple eliminated Target Display Mode
support from macOS 10.14 Mojave. In order
to use your iMac as a display, it has to be
both the correct model year and have
macOS 10.13 High Sierra or an earlier
version of macOS (or Mac OS X) installed.
The Mac that uses the display of an
iMac of the correct vintage with the correct
macOS version installed has its own
requirements: The controlling Mac must be
a model released in 2019 or earlier and
must have macOS 10.15 Catalina or earlier
installed. macOS 11 Big Sur apparently
modified the capability for Intel Macs to
target an otherwise qualifying iMac as a
display, and the Apple silicon M1 Macs can
only run Big Sur—or, soon, Monterey.
Update: A few readers with Big Sur
installed have written in to say that they
can, in fact, still control an iMac with their
Big Sur Mac. However, we’ve also heard
from other readers who were frustrated
they could not. (One reader said that it
only worked after pressing Command-F2
repeatedly on the iMac, sometimes a few
seconds apart, which may have overcome
the iMac’s resistance.) Apple only supports
Catalina and earlier with this feature, which
means the company could fully disable it
in an update to Big Sur without
contradicting its support documents.HOW TO UNLOCK YOUR MAC
WITH ITS RECOVERY KEY AND
F I L E VAU LT AC T I V E
FileVault hardens macOS by wrapping a
layer of login protection around your data.
When FileVault is enabled, the data on
your startup drive is not immediately
available, with just a password between an
attacker and your files. That’s a dangerous
situation if someone has physical access
to your computer—either in your home or
office or because they’ve stolen it—as
there are both known and not-yet-
discovered methods by which an attacker
could try to mount the drive and read files.
FileVault on all Macs puts an additional
bar in place: Your drive is encrypted and
its files are unavailable until there’s been a
successful macOS login. At that point, the
Mac enters its normal operation mode.
(With Intel Macs with a T2 Security Chip
and on all M1 Apple silicon Macs, the
drive’s contents are always encrypted, but
the drive is mounted at startup without an
additional step if you haven’t enabled
FileVault. Read our explanation from last
year [fave.co/3DAzTX8] about how T2 and
M1 Macs interact with FileVault.)