There are no valid SQL Server 2014 features to perform this operation
That's really to less on informations.
How did you start the uninstallation?
Is there a SQL Server 2014 installed at all?
My guess: There was an in-place upgrade 2014 to a newer version like 2016-2019, and now you run 2014 uninstallation? That don't work, even because it makes no sense.