I don’t know how you went about installing davinci, but if you added a repo or ppa that is incompatible with the version you had, apt would try to resolve it by removing everything incompatible.
Easiest way to fix it would be to reinstall Kubuntu and all the packages you had, while keeping your old home partition/folder. That way all your data, downloads and most of the configs will stay.
The installer used to have a checkbox for that somewhere, at least back in the day when I used Kubuntu. Afaik it would automatically detect that a home already exists, even if it is not on a seperate partition.
But just to be extra safe, I’d recommend just live booting some other OS and backing up your home to an external drive.