What practical options exist for running 32-bit applications on Catalina (macOS 10.15)?
I guess it depends on what you mean by realistic options?

In summary though, the three best options are:


use a virtual machine (as you've already mentioned)
use a second boot disk (e.g. an external drive, another partition on your internal drive, etc) that has another version of macOS installed and boot from that as required
have a second Mac with another version of macOS installed. Depending on the Mac model, with this option you could also use the Mac in Target Disk Mode to boot your primary Mac if/when required.


Which ones of the above are the most realistic will depend on your individual circumstances.