Yes, make sure the 19 is turned off.
After restoring the backup: Zigbee devices need to be repaired (web app: right click and select “repair”), or, if it doesn’t work, re-pair the device by pushing it’s pair button
As long as you don’t start it when the the 23 is running. 2 devices running the same flows in parallels can get odd results.
The backup will be incompatible (=assumption).
And Zwave and zigbee devices won’t be recognized.
As a failover Homey, you’d use a identical model.
However, you can export/import any advanced flow though between old/new & new/old Homey.
When you stop backupping the 19, but keep it in your account, the last 7 backups will be kept (unless you delete them):
Summarised: you’ll need a Pro 23 as a real, fully usable failover machine. In my humble opinion of course.
EDIT
Just found this thread: even restoring Pro 23 backup to another Pro 23 doesn’t go smooth at all times. Depending on what brands, protocols & devices you use of course:
