February 2022 • Macworld 103seventh- and eighth-generation
models) had the right graphics
circuitry for this Target Display
Mode feature.
Since 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.
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
that 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
FILEVAULT ACTIVE
FileVault hardens macOS by wrapping
a layer of login protection around
your data. When FileVault is enabled,
the data on your start-up 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 they’ve stolen
it – because there are 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