In macOS 10.13 (High Sierra), Apple started warning users about 32-bit applications by saying those applications were "not optimized" for their Macs. The warnings continued in macOS 10.14 (Mojave). Starting with macOS 10.15 (Catalina), 32-bit applications will cease working altogether.
Hopefully, vendors still producing 32-bit applications for Macs will get their acts together and create 64-bit versions soon.
In the meantime, you might want to check your Macs for what 32-bit applications they have installed so you can pressure vendors to update their apps, start looking for 64-bit alternatives to those apps, or consider whether you even still need to use those apps.
Checking for 32-bit apps on an individual machine
I'm not sure how useful this would be to Mac admins, but you can check for 32-bit applications on a single machine by going to System Information.app
Then scroll down on the left side to find, under Software, Applications.
It might take a while for the list to load.
Once the list is loaded, you can sort by 64-bit (Intel), and then sort again, so all the No entries are at the top.
Checking for 32-bit apps for multiple machines via MunkiReport
If you want to query the MunkiReport database directly, you can also run
ORDER BY name, path
Thanks to eholtam and gmarnin on the MacAdmins Slack for pointing me to the right place in MunkiReport.