So if you want to buy a new Mac in the not too distant future and you also want to be able to use 32 bit apps without screwing around with VMs et al., am I right in assuming you pretty much should buy before roughly Oct when Catalina comes out? Is there a specific time it usually takes Apple to start putting the new version of macOS onto shipping hardware? If a Mac was originally released with Mojave, but ships after Catalina came out and already has Catalina installed, is there any simple way to get Mojave onto it?
In general, it’s the exact hardware model that determines the earliest system it can run. How easy it is to install that earlier system version varies. On older hardware it’s usually easy though you’ll need a bootable installer, but with the file system change it can be a bit more involved.
I got my 27" iMac last May (in case they updated the hardware during WWDC as they sometimes do) because I wanted to be able to run Sierra on it. it shipped with High Sierra, and since it has an SSD, it was formatted with APFS. I had to boot into a bootable High Sierra installer on an external drive to be able to reformat the drive to unadulterated HFS. Once that was done I could use a bootable Sierra installer on an external drive to install it.
This isn’t guaranteed to work. It would be possible for apple to do a minor hardware update near the time that a new system ships which could prevent installing the earlier version. If you want to absolutely sure, you should buy the new mac somewhat in advance of the Catalina release.
Unless you’re hoping for a particular model to get a hardware refresh right before a new system comes out, it doesn’t cost any more to just buy the new mac now and be certain you’re getting what you need, and you’d get to use the presumably faster hardware now instead of later. Plus it would be what you want out of the box with no fuss or worries.
Thanks. Solid advice.
It’s my wife’s old 2010 MBP that needs a replacement. I think the recently refreshed MBA would be just fine for her, but she’s in no hurry to actually spend the money. (We’d rather spend it on a lavish vacation in Japan.) My main concern is that we need to update her Mac before Catalina comes out. IIRC that’s around Sep.