I have successfully install Catalina to an external USB flash drive.
I have been booting Catalina from external USB flash drive for several months.
As an update was available for Catalina, I chose to install the update.
My MacBookAir rebooted, Catalina update was attempted during system startup.
Catalina update failed at 99%.
What does the apple community recommend for resolving this issue?
MacBook Air 13", macOS 10.14
You didn't mention how much free space it has left. If the update was to work at all it should have at least 15GB left. However, I don't know how reliable running the OS is or for how long it would be off a flash drive.
Do you actually mean a flash drive or an SSD? If you mean a flash drive, how large is it and how much free space is on it?
I'm using a 128GB Samsung BAR Plus USB 3.1 Flash Drive rather than an SSD. Link to purchase & specs:
https://www.amazon.com/Samsung-BAR-Plus-128GB-MUF-128BE3/dp/B07BPK3XWW
upgrade Catalina installed on external USB flash drive
