In June 2017 Apple wrote

At WWDC 2017, we announced new apps submitted to the Mac App Store must support 64-bit starting January 2018, and Mac app updates and existing apps must support 64-bit starting June 2018.

Open System Information (the Apple icon in the menu bar), and look in Software > Applications for the 64-bit column entry for your software. Check with the developer. When the June-ish update of macOS comes along it will natter you about 32-bit applications, and at a future time macOS will not open the application at all.

Is anyone still releasing 32 bit apps for the mac? The last time I shipped a 32 bit Apple application was around 2012.

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Andy Brice
https://www.hyperplan.com

Well, obviously there are people who do that. In my list of applications release in the past six months, and that are still flagged as not-64 bit, are all of the Adobe Creative Cloud account management tools (AAM), Synology utilities, Garage Band, CrossOver, the Kindle app, Mathematica, all the Concept Draw apps, and TheBrain 9. The last has attempted several times to issue updates that register as 64-bit and has failed every time, including yesterday.

Andy Brice wrote:

Is anyone still releasing 32 bit apps for the mac? The last time I
shipped a 32 bit Apple application was around 2012.

I had a look on my laptop. There is quite a bitf stuff on there that is 32 bit as well, which is a surprise. Especially when it is big companies like Adobe and Microsoft.

--

Andy Brice
https://www.hyperplan.com

32bit files on 64bit Windows:

c:\Windows\SysWOW64

https://en.wikipedia.org/wiki/WoW64

The situation on Windows is a bit different in that MS are still selling both 32 and 64 bit versions of Windows. Whereas there hasn't been a 32 bit version of macOS for some time (2011?).

I still ship 32 bit applications on Windows as they run fine on both 32 and 64 bit versions of Windows and there seems to be no real advantage to shipping both 32 and 64 bit versions for my software (just more testing and the possibility of user confusion). For some applications (e.g. those that require lots of memory) having a 64 bit address space might be a real advantage.

--

Andy Brice
https://www.hyperplan.com

CrossOver, the Kindle app,

Mathematica, all the Concept Draw apps, and TheBrain 9. The last has
attempted several times to issue updates that register as 64-bit and has
failed every time, including yesterday.

Oh boy....Crossover is very important application.
I need to keep a note not to update my mac. I don't want to screw Crossover.

Thank you for this note guys.

Update: I've learned that the System Information display data is cached and so an application update (like I did to TheBrain 9) does not necessarily update the cache and false negatives are possible. Rename the application and refresh the cache (⌘R) or look at the running application in Activity Monitor with the "Kind" column viewing. Doing both of these, showed me that TheBrain 9 is *now* 64 bit.