Catalina dropped support for older apps which are 32bit apps.
do a google search for:
How do downgrade from catalina
You will see several video by the same person. He has revised the procedure over time. Don't know which to choose. I've never had a need. This may be the latest version:
https://www.youtube.com/watch?v=RR9aWqwb5Zs
.....
You not running your business correctly. You should have a bootable clone of your system. You should have a current startup drive and a prior startup drive. You should clone the current startup drive to the prior. Upgrade. Thus if you run into an issue, you can boot from your prior system and continue working.
...
I clone with Carbon Copy Cloner.
Clone drive or partition
Apple's Time Machine
https://support.apple.com/en-us/HT201250
Carbon Copy Cloner will copy your startup drive to an
external drive. You can boot from the external drive to verify
that you have a good clone. When you upgrade your existing startup
drive, you can at any time boot from your external drive and go back
to your existing system.
http://www.bombich.com/software/ccc.html
SuperDuper is the wildly acclaimed program that makes
recovery painless, because it makes creating a fully bootable backup
painless. Its incredibly clear, friendly interface is
understandable, easy to use, and SuperDuper's built-in scheduler
makes it trivial to back up automatically. And it runs beautifully
on both Intel and Power PC Macs!
Give SuperDuper a workout on your own system. Clone to your heart's
content — for free. See what else is possible. When you're convinced
that SuperDuper is a terrific solution — and a great value at $27.95
— you can register right from the application and start using its
advanced features immediately!
http://www.shirt-pocket.com/SuperDuper/SuperDuperDescription.html
R