For those that have been following along, 64-bit is not that new.
Apple has been talking to developers about the 64-bit transition
for several years. Chances are your apps have already been updated
to take advantage of the architecture.
However, if your apps haven’t been updated, they won’t run on the
new operating system. You should be aware of that before you
In typical Apple fashion, the company has made it easy to find out
if you’ll have a problem with your apps. In your current macOS,
you can go to About this Mac > System Report > Applications and
get a list of all applications and whether they are 64-bit or not.
If you decide not to do that and try to install macOS Catalina,
the installer will post a warning that some of your apps are not
compatible with the new operating system. It will also give you a
list of these apps. You can decide to stop the install process and
contact the developers about updates or continue, knowing those
apps won’t work.
I don’t have any remaining apps of consequence that are 32-bit only, but it’s certainly worth checking before you upgrade.