The configuration for the included Kup backup for Neon seem very straightforward. I don’t see many references to issues in the forums so I assume that my challenge is due to pilot error. I am backing up to a mounted USB drive with several TB of space and backup seems to connect. However, there is a red badge on the status display.

I would sincerely appreciate any suggestions regarding possible cause.

I am running the following:
Operating System: KDE neon 5.27
KDE Plasma Version: 5.27.3
KDE Frameworks Version: 5.104.0
Qt Version: 5.15.8
Kernel Version: 5.19.0-38-generic (64-bit)
Graphics Platform: Wayland
Processors: 8 × Intel® Core™ i7-4790T CPU @ 2.70GHz
Memory: 15.6 GiB of RAM
Graphics Processor: Mesa Intel® HD Graphics 4600
Manufacturer: HP
Product Name: 410-019
System Version: 1.00

There is lots of space on the destination identified by Kbackup. I am at a loss. I even did a fresh bare metal install and have the same issue. GPT suggested the following but everything seems to check out.

[The red badge on the status display of Kup backup for Neon indicates that there is an error with your backup. [The error could be due to various reasons such as insufficient space on your USB drive, incorrect configuration settings, or a bug in Kup] [You can try checking if you have enough space on your USB drive and if your configuration settings are correct]. [If that doesn’t work, you can try reinstalling Kup or reporting a bug]

Don't get me wrong but why would anyone entrust anything KDE with something important like backups?

How about Borg (cli) or Vorta (gui) or something else?

https://alternativeto.net/software/kup-backup-system/?license=opensource

Fortunately, I got some helpful advice in another forum and was able to solve the issue. Even though the target drive was mounted and available, the destination folder had to already exist. If it was missing, the application failed with no explanation. The expectation that the application would create the folder in it's absence was wrong. A request for a feature to create the missing folder or at least provide an error message explaining the failure has been made to the project team.