I am a consultant and I am seeing a number of failed Catalina upgrades that leave the user's hard drive in a dreadful state. The install repartitions the drive into 2 volumes, system and data, and if there is not enough room or some other hiccup it leaves the computer unable to boot and a data recovery is required to restore the files. Often the people that have these issues are the same ones that do not have a time machine backup meaning many hours work to get everything back...... yuk !