External drive not supported

Computer: 2016 MBP, 10.14.6 (not upgraded due to necessary software won’t run on 10.15).

I have an external 500 GB SandDisk SSD that I use for Carbon Copy Cloner to keep a running backup.

Every time I start my MBP, Finder complains that the disk is incompatible : "This disk uses features that are not supported on this version of macOS."

The disk performs as expected. I’ve run the repair routine from Disk Utility.

Does anyone know why Finder is complaining? Possibly exactly the features not supported? And less importantly, a way to perhaps avoid the annoying warning on each startup?