Earlier this year we discussed how Apple promoted new versions of macOS on the App Store on older Macs that were originally incompatible. Now, with macOS Mojave released, Apple is still doing the same, and this time it's even worse.
On my own 2008 iMac, I received a notification about "Upgrade to macOS Mojave," complete with a brief description of some great new features
After I opened the Mac App Store, I clicked The "Download" button to start my update just to get an error message "This version of macOS 10.14 can not be installed on this computer."
The error message was about this vague as it is – nothing about my specific model that is incompatible with macOS Mojave. Honestly, if I had not known that my 2008 iMac was incompatible with Mojave (as is probably the case with many older Mac owners), I would easily have taken this as a verbatim error message and assumed that it was a problem with mine Mac.
That's pretty irresponsible to Apple. I understand that they want to promote the latest and greatest software to get customers to buy a newer Mac, but nowhere does it specifically tell me that my older Mac is not compatible with Mojave. At least in a situation like this, they have to make that clear.